Identification and multi-environment validation of resistance to Botrytis fabae in Vicia faba

The aim of this work was to find new sources of resistance to chocolate spot disease, and to validate their stability across different environments. In order to do so, a collection of 307 accessions of Vicia faba was screened for resistance to Botrytis fabae under field conditions; stability of resistance of the 40 most-resistant accessions was tested in a multi-location experiment in Austria, Chile, Egypt, France and Spain over two field seasons. Although complete resistance was not found, nine accessions showed interesting levels of incomplete resistance (ranging from 10 to 20% of average severity across environments, maximum average severity being 47.9%). Genotype × environment interaction accounted for 22% of the sum of squares of the multi-environment evaluation, revealing instability of the phenotypic expression across environments. This usually hampers the efficiency of selection and reduces the adaptability of the plant material. Three accessions stand out for their consistent resistance, both in terms of reduced disease severity and high stability, which make them good candidates for breeding programs. As for environments, those with the highest total severity mean were the most discriminant between accessions. In contrast, those with lower severity means were the most representative of the whole range of environments. It can be concluded that validation of resistance to chocolate spot in different environments is an essential step when screening for material of interest and should be taken into account for further works.     

Evaluation of soybean for resistance to soybean rust in Vietnam

Soybean rust, caused by Phakopsora pachyrhizi Sydow, is a severe foliar disease of soybean [Glycine max (L.) Merr.] that occurs throughout most soybean producing regions of the world. The objective of this research was to evaluate selected soybean genotypes for resistance to soybean rust in Vietnam. Five field experiments in Vietnam were completed from 2006 to 2009. The area-under-the-disease-progress-curve (AUDPC) was calculated for each soybean genotype based on four disease assessments taken during the reproductive growth stages. AUDPC units among soybean genotypes in each experiment differed (P < 0.05). Over the five experiments, the resistant check DT 2000 was most often the genotype with the lowest AUDPC units while the sources of rust resistance (Rpp1-5) did not always have low AUDPC units in each experiment, although PI 230970 (Rpp2) appeared to be more stable. A few genotypes with non-characterized genes for resistance, such as PI 398998, PI 437323, and PI 549017, had the lowest AUDPC units in at least one of the experiments. These genetic resources may be useful for host plant resistance studies and breeding soybeans for rust resistance in Vietnam and other locations like Brazil and the United States that have more recently been inundated with soybean rust. A significant (P < 0.001) experiment × genotype interaction was found when the AUDPC data of 14 soybean genotypes tested in Experiments 1, 2, and 3 were combined and analyzed. This result indicates the potential importance of changing fungal races and/or biotypes that occur in the rust population.     

Evaluation of the yield potential and physicochemical properties of the biomass of Salix viminalis × Populus tremula hybrids

This study presents the characteristics of four Salix viminalis × Populus tremula hybrids, produced for the first time in the world grown in a three-year field experiment. Shoot weight per plant and major biomass yield components, including plant height, number of shoots per rootstock and shoot diameter, were determined. The infection severity caused by leaf rust (Melampsora sp.) was also evaluated. The biomass of three-year-old hybrid plants was subjected to chemical analyses and calorimetric tests to determine the energy value of biomass as solid fuel. Among the studied genotypes the highest yield was achieved by one of the studied hybrids. Its biometric parameters did not differ significantly from the standard genotype, and they were superior to the parameters of the maternal form. All Salix × Populus hybrids were more susceptible to rust infections than their maternal form and one hybrid was more resistant to infections caused by fungi of the genus Melampsora. Two hybrids have optimal biomass parameters as regards both calorific value and amount of carbon, hydrogen, sulfur and nitrogen.     

Genetic analysis of field resistance to tan spot in spring wheat

Tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs., is an important constraint to wheat (Triticum aestivum L.) yield in many countries. Since the inheritance of field resistance to tan spot is poorly understood, this study was conducted to determine the genetic control of resistance in the field. Resistance was measured as disease severity caused by P. tritici-repentis race 1 in four crosses involving five wheat parents: parent 1 (P₁) = catbird; parent 2 (P₂) = Milan/Shanghai-7; parent 3 (P₃) = Alondra/Coc//Ures; parent 4 (P₄) = Bcb//Dundee/Gul/3/Gul); parent 5 (P₅) = ND/VG9144//Kal/BB/3/Yaco/4/Chil. P₁, P₂ and P₃ were resistant and P₄ was moderately resistant, whereas P₅ was susceptible to tan spot. The F₂-derived F₃ families and the parents were field evaluated at El Batán, Mexico, in 1996. When all the plants within a F₃ family expressed low levels of disease severity similar to that of the resistant parent it was classified resistant (R), otherwise the progeny was classified as susceptible (S). The progeny of the three crosses of the susceptible parent with the resistant and moderately resistant parents P₂, P₃, and P₄ segregated as 3R:13S whereas the progeny in the cross with P₁ showed a segregation ratio of 1R:15S. This suggests that each resistant parent possessed two genes conditioning resistance to tan spot severity caused by P. tritici-repentis race 1. Information on the inheritance of resistance measured as disease severity on adult plants under field conditions is of practical importance for wheat breeding programs seeking improvement in tan spot resistance.     

Fire blight (Erwinia amylovora) resistant/susceptibility of native apple germplasm from eastern Turkey

This study aimed to determine the resistance/susceptibility to fire blight of apple germplasm resources from the province of Erzincan in eastern Turkey. In total, 32 native apple accessions from four regions within the province were tested under greenhouse conditions by inoculating the shoot tips with pathogenic bacterium. Shoot tips were wounded for inoculation. Genotypical susceptibility index (GSI%) values were computed for each genotype based on the length of the lesion that developed on each shoot. Accessions were grouped into five classes of resistance/susceptibility, as follows: Class A (resistant); Class B (moderately resistant); Class C (moderately susceptible); Class D (susceptible); and Class E (highly susceptible). GSI% values differed significantly among accessions (p < 0.01). Five accessions received a rating of Class A, and 7 accessions received a rating of Class B. This was followed by 9 accessions with a rating of Class C, 5 accessions with a rating of Class D and 6 accessions with a rating of Class E. The findings of this study are expected to contribute to breeding efforts with respect to apple resistance to fire blight.     

Understanding the relationships between genetic and phenotypic structures of a collection of elite durum wheat accessions

A collection of 191 durum wheat accessions representing Mediterranean Basin genetic diversity was grown in nine different environments in four countries, with productivities ranging from 0.99 to 6.78 t ha⁻¹. The population breeding structure comprised eight genetic subpopulations (GSPs) using data derived from 97 evenly distributed SSR markers. The phenotypic structure was assessed: (i) from the mean values of six agronomic traits across environments (multivariate), and (ii) from data representing each trait in each environment (univariate). Mean daily maximum temperature from emergence to heading was significantly (P < 0.05) and negatively associated to yield, accounting for 59% of yield variations. Significant but weak relationships were obtained between the genetic similarities among accessions and their overall agronomic performance (r = 0.15, P < 0.001), plant height (r = 0.12, P < 0.001), spike–peduncle length (r = 0.06, P < 0.01) and thousand kernel weight (r = 0.03, P < 0.05), suggesting a very low possibility of prediction of the agronomic performance based on random SSR markers. The percentage of variability (measured by sum of squares) explained by the environment varied between 76.3 and 98.5% depending on the trait, while that explained by genotypes ranged between 0.4 and 12.6%, and that explained by the GE interaction ranged from 1.1 to 12.5%. The clustering of the accessions based on multivariate phenotypic data offered the best explanation of genotypic differences, accounting for 30.3% (for yield) to 75.1% (for kernel weight) of the observed variation. The genotype × environment interaction was best explained by the phenotypic univariate clustering procedure, which explained from 28.5% (for kernel weight) to 74.9% (for days to heading) of variation. The only accessions that clustered both in the genetic dissimilarities tree and the tree obtained using Euclidean distances based on standardized phenotypic data across environments were those closely related to the CIMMYT hallmark founder ‘Altar 84’, the ICARDA accessions adapted to continental-dryland areas, and the landraces, suggesting that genetic proximity corresponded to agronomic performance in only a few cases.     

Manihot flabellifolia Pohl,wild source of resistance to the whitefly Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae)

Aleurotrachelus socialis is one of the most important pests of cassava (Manihot esculenta Crantz) in the Neotropics. In Colombia, high whitefly populations can reduce crop yields by 79%; and although the farmers intensify the use of insecticides, this practice is highly contaminating, costly and leads to the development of resistance in the insect. An alternative for managing whitefly populations is to develop genetically resistant varieties. Wild parents of Manihot are a useful source of genes against pests for the cultivated species of cassava. Based on prior research that showed the existence of moderate-to-high levels of resistance to A. socialis in Manihot flabellifolia, a wild species of cassava, this study was proposed to characterize this new source of resistance, evaluating the biology and demographics of A. socialis on eight accessions of M. flabellifolia, a susceptible check (CMC-40) and a resistant (MEcu72) check. The averages of A. socialis longevity and fecundity on the accessions were not significantly different to MEcu72, but different from CMC-40 (P < 0.05). Development time was not significantly different, ranging from 35–40 days on accessions and MEcu72 and 33.5 days on CMC-40 (P < 0.05). In contrast, the population growth rate (r_m) was significantly lower on the M. flabellifolia accessions, with Fla 61 standing out with a growth rate 98 and 99% less than that obtained on MEcu72 and CMC-40, respectively. Once the resistant levels have been identified to A. socialis on the M. flabellifolia accessions, interspecific crosses of M. esculenta subsp. M. flabellifolia and backcross programs could be developed to incorporate the desirable characteristics from the wild relatives into elite progenitors of M. esculenta.     

Adaptation of landrace and variety germplasm and selection strategies for lucerne in the Mediterranean basin

Lucerne (Medicago sativa L.) can enhance the economic and environmental sustainability of crop-livestock systems in the western Mediterranean basin, but requires improved adaptation to stressful environments because of a predicted shortage of irrigation water and climate change. This study reports on three-year dry matter yields of five landraces from Morocco, Italy and Tunisia and seven varieties from France, Italy, Australia and USA assessed across 10 agricultural environments of Algeria, Tunisia, Morocco and Italy of which four were rainfed, one was continuously irrigated (oasis management), and five were irrigated but adopted a nine-week suspension of irrigation during summer. Our objectives were targeting cultivars to specific environments, and assisting regional breeding programmes in defining adaptation strategies, genetic resources and opportunities for international co-operation. The crop persisted well in all environments, but environment mean yield was strictly associated (P < 0.01) with annual and spring-summer (April–September) water available. Rainfed cropping implied 42% lower yield with 61% less spring-summer water available relative to irrigation with withheld summer water across three sites hosting both managements. All of these sites showed genotype × management interaction (at least P < 0.10). Cross-over genotype × environment (GE) interaction between top-yielding cultivars occurred across the 10 environments. Total number of harvests (range: 9–23), soil salinity as measured by electrical conductivity (range: 0.20–6.0 dS m⁻¹), and average spring-summer water available (range: 102–932 mm) were selected as significant (P < 0.05) environmental covariates in a factorial regression model explaining 53% of GE interaction variation. This model was exploited for targeting cultivars as a function of site-specific levels of these factors. Its indications agreed largely with those of an additive main effects and multiplicative interaction model with two GE interaction principal components. An Italian landrace exhibited specific adaptation to severely drought-prone environments, whereas landraces from north Africa were not adapted to such environments. One Moroccan landrace was specifically adapted to high number of harvests (partly reflecting frequent mowing). One variety selected for salt tolerance, and one Moroccan landrace, were specifically adapted to salt-stress environments. Environment classification as a function of GE interaction effects indicated three groups which may be object of specific breeding: (i) rainfed or irrigated environments featuring limited spring-summer water available (<350 mm), nil or low soil salinity, and moderate to low number of harvests; (ii) salt-stress environments; and (iii) environments characterized by high number of harvests.     

Genotype × environment interaction for zinc and iron concentration of wheat grain in eastern Gangetic plains of India

Zinc and iron are important micronutrients for human health for which widespread deficiency occurs in many regions of the world including South Asia. Breeding efforts for enriching wheat grains with more zinc and iron are in progress in India, Pakistan and CIMMYT (International Maize and Wheat Improvement Centre). Further knowledge on genotype × environment interaction of these nutrients in the grain is expected to contribute to better understand the magnitude of this interaction and the potential identification of more stable genotypes for this trait. Elite lines from CIMMYT were evaluated in a multilocation trial in the eastern Gangetic plains (EGP) of India to determine genotype × environment (GE) interactions for agronomic and nutrient traits. Agronomic (yield and days to heading) data were available for 14 environments, while zinc and iron concentration of grains for 10 environments. Soil and meteorological data of each of the locations were also used. GE was significant for all the four traits. Locations showed contrasting response to grain iron and zinc. Compared to iron, zinc showed greater variation across locations. Maximum temperature was the major determinant for the four traits. Zinc content in 30–60 cm soil depth was also a significant determinant for grain zinc as well as iron concentration. The results suggest that the GE was substantial for grain iron and zinc and established varieties of eastern Gangetic plains India are not inferior to the CIMMYT germplasm tested. Hence, greater efforts taking care of GE interactions are needed to breed iron and zinc rich wheat lines.     

Pre- and post-inoculation activity of a protectant and a systemic fungicide for control of anthracnose fruit rot of strawberry under different wetness durations

A protectant fungicide (Captan, a.i. captan) and a systemic fungicide (Switch, a.i. fludioxonil + cyprodinil) were evaluated as pre- and post-inoculation applications for control of anthracnose fruit rot (AFR), caused by Colletotrichum acutatum, under a short (6 or 8 h) or long (18 or 24 h) wetting period. Evaluations were conducted for two seasons in Maryland and for two seasons in Florida. Both Captan and Switch were very effective for control of AFR when applied prior to inoculation, but control was more effective under the shorter wetting period. Switch was as effective when applied 4, 8, or 24 h post-inoculation as when applied before inoculation, but control was better under the short wetting period. Captan was effective when applied 4 or 8 h after inoculation under the short wetting period, but was ineffective at 24 h post-inoculation. Post-inoculation sprays of Captan were ineffective at any time under the long wetting period. The post-infection activity of Switch allows greater flexibility for managing AFR when fungicide applications are scheduled based on weather-based decision-support systems.     

Phenotypic identification of peanut germplasm for resistance to southern stem rot

Southern stem rot, caused by Sclerotium rolfsii Sacc., is a destructive soil fungal disease of peanut in China and other countries. To evaluate resistant germplasm, a total of 256 peanut accessions were investigated on their resistance to southern stem rot in 3 environments by artificial inoculation. Variance analysis indicated that disease index was significantly influenced by environment, genotype and genotype ​× ​environment interactions. Peanut accessions of var. vulgaris type exhibited higher resistance to southern stem rot. Disease index was significantly negatively correlated with linoleic acid content, while positively correlated with oleic acid content. Six resistant accessions were identified, including Hua 28, Shandongzai, ICG 6326, Quanhua 7, Quanhua 9 and Guihua 836, with their disease indexes under 40 and mortality were less than 30% in the three environments. The identified resistant accessions showed the great potential to be applied in resistant peanut breeding, and would be good genetic resources for enhancing the resistance to southern stem rot.     

Morphological characteristics and composition of lipophilic extractives and lignin in Brazilian woods from different eucalypt hybrids

The morphological and chemical characteristics of the woods from several eucalypt hybrids from the Brazilian Genolyptus program were studied. The hybrids selected for this study were Eucalyptus grandis × E. urophylla (IP), E. urophylla × E. urophylla (U1 × U2), E. grandis × [E. urophylla × E. globulus] (G1 × UGL), and [E. dunnii × E. grandis] × E. urophylla (DG × U2). The analyses of the lipophilic extractives indicated a similar composition in all eucalypt hybrids, which were dominated by sitosterol, sitosterol esters and sitosteryl 3β-d-glucopyranoside. These compounds are responsible for pitch deposition during kraft pulping of eucalypt wood. Some quantitative differences were found in the abundances of different lipid classes, the wood from U1 × U2 having the lowest amounts of these pitch-forming compounds. The chemical composition and structure of lignins were characterized by Py-GC/MS and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p-hydroxyphenyl units in all the woods, with the highest S/G ratio for G1 × UGL. The 2D-NMR spectra gave additional information about the inter-unit linkages in the lignin polymer. All the lignins showed a predominance of β-O-4′ ether linkages (75-79% of total side-chains), followed by β-β′ resinol-type linkages (9-11%) and lower amounts of β-5′ phenylcoumaran-type, β-1′ spirodienone-type linkages or β-1′ open substructures. The lignin from the hybrid G1 × UGL presented also the highest proportion of β-O-4′ linkages, and therefore, it is foreseen that the wood from this hybrid will be more easily delignifiable than the other selected Brazilian eucalypt hybrids. In complement to these chemical analyses, the morphological characterization of fibers, vessels and fines revealed that hybrid eucalypt clone DG × U2 presented the most interesting properties for the manufacture of paper pulps and biofuels.     

Adaptation strategy,germplasm type and adaptive traits for field pea improvement in Italy based on variety responses across climatically contrasting environments

A pea breeding strategy is required to cope with the large climatic variation featuring south-European environments. Thirty-seven recent cultivars bred by 21 European or Australian institutions were grown in two climatically contrasting Italian sites (Lodi, subcontinental; Foggia, Mediterranean), two cropping years per site and two sowing times per year, to define various elements of this strategy. The study assessed: (i) the impact of genotype × environment (GE) interaction due to spatial and temporal factors on the consistency of top-yielding cultivars; (ii) the similarity between environments for GE effects and its implications on adaptation strategies; (iii) the extent of genotypic and GE interaction effects, and the relationship with adaptive responses, for various morphophysiological traits; (iv) the adaptation pattern and the combination of adaptive traits featuring three germplasm types, i.e. European spring and winter types, and germplasm selected in Mediterranean environments; (v) the predicted efficiency of direct and indirect selection procedures for grain yield. The geoclimatic area had a major impact on crop yield (5.15 t/ha in Lodi vs. 2.52 t/ha in Foggia) but tended to affect GE interaction less than time or year of autumn sowing, suggesting to breed for wide adaptation. Top-yielding cultivars as modeled by additive main effects and multiplicative interaction were environment-specific. On average, spring and winter materials outyielded the Mediterranean germplasm but the spring type, characterized by wide entry variation, included most widely- and specifically-adapted top-yielding cultivars. Cold-tolerant spring-type germplasm is preferable to breed for wide adaptation as it may combine high yield potential with adaptation to winter cold and terminal drought and heat stress. Lodging susceptibility, harvest index, onset and duration of flowering, and canopy height at maturity assessed in individual environments showed moderate to fairly high broad-sense heritability on a plot basis (h² > 0.20) and tended to correlation with yield over test environments (r ≥ 0.20). An indirect selection index including harvest index and canopy height exhibited about 20% greater predicted efficiency than direct selection for yield when using one selection environment and could be preferred for early selection stages. Direct yield selection in late selection stages should ideally be performed across 2 years in two environments that contrast for geoclimatic area and time of autumn sowing.     

Analysis of starch swelling power in Australian breeding lines of hexaploid wheat (Triticum aestivum L.)

Starch is the major component of wheat (Triticum aestivum L.) grain and is composed of two large glucan molecules, amylose and amylopectin. The ratio between the two polymers types influences the water absorbing properties of starch upon heating, and thus affects the end-use of grain and purified starch. In this study, we evaluated the starch swelling power (SSP) values in seven wheat populations developed from crosses involving low-SSP lines. Analysis of starch produced by the F₂ generation plants showed that the largest SSP variation (11.4–16.2) and lowest SSP mean (13.9) was obtained for a population derived from doubled haploid lines SM1028 (SSP = 14.5) and VK306 (SSP = 13.6). The population of 360 lines was advanced by single seed descent to the following generations for further studies. Starch analysis of grain produced by F₄ generation lines in two field locations during 2006 and in a greenhouse environment during 2005 showed that SSP values were relatively stably inherited. The average broad-sense heritability was 73% and significant (P < 0.001) genotype × genotype and genotype × environment interactions were seen. Starches with the highest and lowest SSP values were inversely related to amylose concentration determined by high pressure liquid chromatography (HPLC)–size exclusion chromatography (SEC) of debranched starch. Developed lines with the lowest SSP values surpassed 40% in apparent amylose concentration. The study illustrates that screening for SSP in early generations can be used to develop wheat lines with desired starch swelling characteristics.     

Analysis of QTL for resistance to head smut (Sporisorium reiliana) in maize

Head smut of maize, caused by the fungus Sporisorium reiliana, is an important disease in the temperate maize-growing areas worldwide. In this study, we mapped and characterized quantitative trait loci (QTL) conferring resistance to S. reiliana using a F_2:3 population of 184 families derived from a cross between Mo17 (resistant parent) and Huangzao4 (susceptible). The population was evaluated for resistance in replicated field trials with artificial inoculation of S. reiliana chlamydospores in Gongzhuling of Jilin Province and Harbin of Heilongjiang Province of China, two hot spots of head smut incidence, in 2003 and 2004. Genotypic and G × E variances for disease incidence were highly significant in the population. Heritability estimates for percentage disease incidence in the 2-location and 2-year evaluation ranged from 0.62 to 0.70. Composite interval mapping on a linkage map (1956.1 cM distance; 9.34 cM average interval) constructed with 84 SSR and 135 AFLP markers, identified five QTL, one each on chromosomes 1, 3 and 8 and two on chromosome 2, accounting for 5.0–43.7% of the phenotypic variance across four environments. One major QTL on chromosome 2 explaining up to 43.7% of the phenotypic variance can potentially be used in molecular marker-assisted selection for head smut resistance in maize.     

Monitoring resistance of Helicoverpa armigera to different insecticides used in cotton in Spain

Helicoverpa armigera is the key pest of cotton in Spain, resulting in many insecticide treatments against it. The resistance status of H. armigera to different insecticides currently used in cotton was evaluated in Spain in two different seasons, 1999 and 2004. Four populations were tested in total, two in each season. Toxicological bioassays were conducted in the laboratory, and performed on third instar larvae by topical application of the insecticides. LD₅₀'s were estimated by probit analysis and resistance factors (RF) were calculated at the LD₅₀ level. Four insecticides were evaluated, but only endosulfan reached a moderate resistance level (RF = 11.4), and the others (methomyl, chlorpyrifos and lambda-cyhalothrin) showed low resistance (RF between 1.9 and 6.0). Such results indicate the generally low resistance of H. armigera to most of the insecticides used against this pest in cotton in Spain. Possible explanations for this situation are discussed.     

Response of common wheat varieties to organic and conventional production systems across Italian locations,and implications for selection

Specific breeding for organic systems may help reduce their yield gap relative to conventional systems by exploiting genotype × system (GS) interaction. Likewise, specific breeding for distinct subregions within a region could capitalize on genotype × location (GL) interaction. Grain yield and test weight of common wheat varieties were evaluated under organic and conventional systems in ten locations spanning from northern to southern Italy, with the objectives of: (i) comparing production systems; (ii) investigating the extent of GS and GL interactions and their relationship with genotypic and environmental characteristics; and (iii) preliminarily comparing, in terms of predicted selection gains, different strategies to cope with GS and GL effects. These effects were investigated in the 2-year Data set 1 including seven genotypes. GS effects were also assessed in the annual Data sets 2 and 3 including 13 and 11 genotypes, respectively. The yield reduction of organic systems relative to conventional ones averaged 28% in Data set 1, 29% in Data set 2 and 14% in Data set 3. Organic systems also tended to a modest test weight reduction. Genetic correlations between systems ranged from high to very high (0.88 ≤ r_g ≤ 0.98) for yield and test weight, owing to nil or limited GS interaction. Broad-sense heritability tended to be higher in conventional systems than organic ones for yield in two data sets (mainly due to lower experimental error) while being similar in the two systems in the other cases. Predicted selection gains suggested nil (yield) or very modest (test weight) advantage of direct selection in organic systems relative to indirect selection in conventional systems, when targeting organic systems. The scope for selection only in conventional systems was reinforced when comparing predicted gains for selection scenarios which target both systems in relation to their foreseeable marketing importance. GL effects for yield and test weight were significant and were modeled by additive main effects and multiplicative interaction analysis. Site classification based on GL effects for yield revealed a larger subregion A including northern and central Italy and a smaller subregion B comprising southern Italy, accordingly with previous, independent studies. Yield selection only in subregion A (with indirect selection gain for subregion B) implied slightly higher predicted gain for A (+4%) and much lower gain for B (−24%) relative to independent, direct selection in each subregion. Selection for specific geoclimatic subregions may have greater importance than selection for specific production systems.     

Genotypic response of common bean to natural field populations of bean fly (Ophiomyia phaseoli) under diverse environmental conditions

Bean fly is a significant pest of common bean in semi-arid areas of East Africa. Apart from inadequate moisture in the dry land, bean fly simultaneously contributes negatively thereby adversely affecting bean productivity. The objectives of this study were to (1) identify sources of resistance to bean fly available in landraces, (2) confirm stability of host plant resistance in drought stress and (3) determine the effect of drought stress and seasonal variation on common bean genotypes in relation to bean fly attack for adaptability to the semi-arid areas of East Africa. Sixty four genotypes including landraces, bean fly resistant lines and local checks were evaluated for seed yield, 100-seed weight, days to maturity, plant mortality and pupae in stem in an alpha lattice design with two replications. This was under drought stressed (DS) and non-stressed (NS) environments and two treatments (insecticide sprayed and natural infestation) for three cropping seasons between 2008 and 2009. Genotypes differed in their reaction to natural bean fly attack under drought stressed (DS) and non-stressed (NS) environments over different cropping seasons. However, the effect of bean fly appeared to vary between the long rains (LR) and short rains (SR). It was observed that an increase in number of pupae per stem resulted in a higher plant mortality. The range of seed yield was from 345 to 1704 kg ha⁻¹ under natural infestation and from 591 to 2659 kg ha⁻¹ under insecticide protection. Seed yield loss ranged from 3 to 69%. The resistance of most of the bean fly resistant lines seemed to break down in presence of DS owing to their dismal performance. Screening of genetic resources in common bean to breed for host plant resistance to bean fly offers high potential of success if researchers take full advantage of the diversity available within the landraces.     

Genetic enhancement of Sorghum (Sorghum bicolor (L) Moench) for grain mould resistance: II. Breeding for grain mould resistance

Grain mould causes qualitative and quantitative loss to grain in sorghum. Grain mould resistance is a complex problem as grain mould is caused by complex of fungi and the resistance is governed by many traits. Breeding efforts during the last 3 decades to develop grain mould resistance in high yielding genotypes have not paid many dividends. We developed a strategy to breed for grain mould resistance in high yielding back ground. Twenty five crosses between elite lines and grain mould resistant genetic stocks (susceptible × resistant/moderately resistant and moderately resistant × resistant crosses) were evaluated in F₁, and derivatives performing superiorly for grain mould resistance in F₂-F₄ at physiological maturity were advanced. The early generation material F₂s (10) and F₃s (125) in 6 locations (representing rainy-season-sorghum growing 6 states of India where grain mould is one of the major biotic stresses), and later generations F₄s and F₅s in 3 locations (one location, Parbhani is a hot spot for grain moulds and 2 locations, Hyderabad and Coimbatore in epiphytotic conditions) were evaluated. Only 25 selections out of 384 derivatives in F₄ were superior over locations for grain mould resistance at physiological maturity and harvest maturity (Our simultaneous studies in RILs for grain mould resistance across years and locations have shown that the variation obtained for grain mould resistance at physiological maturity is genetically governed and the grain mould score further gets compounded at harvest maturity depending on rainfall received after physiological maturity). These superior lines were advanced and further evaluated in F₅ and F₆ for grain mould resistance and grain yield. During 2007, out of 25 F₅ derivatives, 12 were on par (scored 3.1-4.4) with resistant check, B 58586 (3.2 score) where as susceptible check, 296 B registered a score of 7.5. GMN nos. 41, 52, 59, and 63 performed on par with resistant check, B 58586 for grain mould resistance over 9 environments. Since we selected for grain mould resistance in early generations at physiological maturity in multi-locations, we could identify superior lines for grain mould resistance. Most of these lines are high yielding and on par with elite check, C43 for grain yield. These lines are distinct for DUS testing traits from grain mould resistant check, B 58586.     

Dynamic patterns of components of genotype × environment interaction for pod yield of peanut over multiple years: A simulation approach

The relative importance of the genotype × year (G × Y), genotype × location (G × L) and genotype × location × year (G × L × Y) interactions has significant implications on the testing strategy of crop breeding lines. The goal of this study was to examine the dynamic patterns of these three interactions for pod yield of peanut using a crop simulation model. Pod yields of 17 peanut lines in the early-rainy, mid-rainy and dry seasons at 112 locations covering all peanut production areas in Thailand were simulated for 30 years (1972–2002) with the Cropping System Model (CSM)-CROPGRO-Peanut. Combined analyses of variance were preformed for individual seasons and for overall seasons, with the number of year incrementally increasing from 2 to 30, and the relative contributions of the individual sources of variation were determined. This procedure was repeated four times with different starting years. The results showed that the environmental effects accounted for the major proportion of the total yield variation, followed by the genotype effects, while the genotype × environment (G × E) effects were rather small. The contributions of the individual sources changed as the number of years in the analysis changed. Increasing number of years in the analyses resulted in an increase in the magnitude of the G × Y and G × L × Y interactions, but a decline in the G × L contribution. The contributions of the G × Y and G × L interactions were greater and more fluctuated in the dry season, while those of the G × L × Y interactions were greater in the mid-rainy season. Notable increases in the G × Y interaction in the dry season were observed in certain years. The decline in the G × L interaction with increasing number of years was closely associated with the increase in the G × L × Y interaction, and both became stable when 6 or more years were included. Several cross-over in the ranks of peanut lines for mean pod yield in two contrasting years were also observed for the mid-rainy season. These results raise a question on the effectiveness of the strategy for using locations to replace years in varietal testing that is normally employed by breeders. The practical limit of multi-year evaluation of crop breeding lines could be overcome by the use of a crop simulation model.