Interpretation of genotype × environment interactions of sugarcane: Identifying significant environmental factors

An understanding of the causes of genotype × environment (G × E) interactions is essential for the implementation of efficient selection and evaluation networks. Currently, studies involving the interpretation of sugarcane (Saccharum spp.) G × E interactions are limited. The objective of this study was to investigate the relative influence of environmental factors on the G × E interactions of sugarcane under rainfed conditions in South Africa through a comprehensive analysis of a multi-environment trial (MET) dataset. Fifteen commercial cultivars were evaluated over 147 environments (trial × ratoon combinations) across the coastal (C), hinterland (H) and midlands (M) regions of the sugar industry. Environments were characterized according to five site covariates (soil depth, clay percentage, organic matter percentage, nitrogen mineralization category, and total available moisture) and nine seasonal covariates (time of harvest, age at harvest, average daily heat units, solar radiation, rainfall, evaporation, and three derived water stress indices).Additive main effects and multiplicative interaction (AMMI) biplots for cane yield (TCANE), estimated recoverable crystal percent (ERC) and tons ERC (TERC) revealed overlapping of C and H environments, while M environments formed unique clusters characterized by specific cultivar adaptabilities. Principal components analysis (PCA) allowed visualization of the covariates determining the regional separation patterns. AMMI interaction principal components axes (IPCA) 1 and 2 scores were correlated to the covariates and showed that harvest age, temperature, and water stress were mainly responsible for separation of M environments from C and H environments on the TCANE and TERC biplots. Time of harvest was identified as an important covariate influencing ERC G × E patterns in the C and H regions. The third water stress index (based on a ratio of observed yields to simulated irrigated yields) was a dominant factor influencing G × E patterns within the C and H regions and was identified as a superior indicator of water deficient environments for future studies. The M trials were characterized by shallower soils with lower total available moisture and greater variability in this regard compared with the C and H trials. Nitrogen mineralization category, organic matter percent, and clay percent were not significantly correlated to IPCA scores, while soil depth was identified as a major site selection criterion in the M region. The M region should be treated as a single mega-environment, while the C and H regions could be combined for future interpretive studies, where covariates should be summarized within growth phases. The results of this study will assist in restructuring the MET network through exploitation and targeting of the relevant environmental factors within the different regions.     

Genetic improvement of sorghum for grain mould resistance: I. Performance of sorghum recombinant inbred lines for grain mould reactions across environments

Grain mould on sorghum is an important disease worldwide, which causes considerable qualitative and quantitative damage. Success in breeding for grain mould resistance has been limited because of many mechanisms governing resistance, complex genetics and environmental influence. Objectives of this study were to characterize 200 recombinant inbred lines (RILs) from a cross between ‘296 B’ (susceptible elite parent) and ‘B 58586’ (resistant parent) for grain mould reaction (GMR) at physiological maturity (PM) and at harvest maturity (HM), and to identify sources of resistance. The RILs were characterized in six environments (3 years × 2 locations) for GMR. Five RILs were identified with GMR on par with the resistant parent across various environments. The results of stability analysis for GMR at PM and HM stages showed difference. At PM, there was a significant genotype (G) × environment (E) (linear) interaction plus significant environmental effects for GMR. However, at HM, there was not a significant G × E (linear) interaction but environment effects were significant for GMR. These indicated that part of variation was predictable at PM while the variation was not predictable at HM as it was entirely influenced by environment. It is concluded that grain mould occurring before PM is influenced by genetics and to some extent by environment while that occurring after PM is influenced by environment. Therefore, host plant resistance would be better assessed at PM than at HM, and identification of quantitative trait loci (QTL) which show consistency in expression across environments, even in diverse environments, would be desirable for marker-assisted selection programs.     

Analysis of host plant resistance to multiple Fusarium species associated with stalk rot disease in sorghum [Sorghum bicolor (L.) Moench]

Fusarium spp. is among the largest and most important pathogen groups that attack major grain crops including sorghum. The objectives of this study were to compare the virulence of Fusarium spp. associated with sorghum and examine the mode of resistance of genotypes to the disease. Eight Fusarium species – F. verticillioides, F. thapsinum, F. andiyazi, F. proliferatum, F. nyagamai, F. pseudoanthophilum, F. brevicatenulatum, and F. pseudonygamai – were studied using three sorghum genotypes under greenhouse condition. Three of these pathogens (F. verticillioides, F. thapsinum, and F. andiyazi) were selected for genetic analysis of resistance under field conditions. Sorghum genotypes with contrasting stalk rot reactions were selected for use in both the greenhouse and field experiments. Two weeks after flowering, plants were inoculated with liquid inoculum culture (5 × 10⁴ conidia ml⁻¹) of the different pathogens. Plants were harvested 4 weeks after inoculation and rated for disease severity on the basis of lesion length and number of nodes crossed by the lesion. Among the pathogens, F. thapsinum resulted in consistently higher disease scores in all genotypes under all environments. Likewise, genotype SC599 showed the greatest and most stable resistance as inbred as well as in hybrid combinations as shown by consistently high GCA for resistance to all pathogen species. We recommend that future screening exercises for Fusarium stalk rot resistance utilize F. thapsinum as the causal organism and include the resistant genotype SC599 as a control.     

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.     

Multiple-disease resistance in Vicia faba: Multi-environment field testing for identification of combined resistance to rust and chocolate spot

The aim of this work was to identify Vicia faba germplasm resistant both to rust and chocolate spot. A collection of 43 accessions of V. faba previously identified as chocolate-spot resistant was evaluated for rust and chocolate spot resistance in Egypt and in Spain. The genotype and genotype × environment (GGE) biplot analyses allowed the selection of 11 accessions resistant to both diseases in those locations. These 11 accessions were evaluated for rust in an additional field trial in Spain, all performing better than the susceptible check. The joint analysis of the 11 accessions in the four field trials where they had been evaluated revealed no significant effects either for genotype, environment or the genotype × environment interaction. They are hence promising sources of resistance, both for their low severities and their stable responses across the studied environments. This collection was also tested under controlled conditions against the Egyptian and the Spanish isolates of rust present in the field trials further underlining the stable performance of these genotypes. Finally, the effect of previous infection with chocolate spot on rust resistance was assessed under controlled conditions and no influence of it was found.     

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.     

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.     

Genetic analysis for resistance to bean fly (Ophiomyia phaseoli) and seed yield among common bean genotypes in a semi-arid environment

Bean fly (Ophiomyia spp.) is a major field pest limiting common bean production in eastern Africa. The genetic enhancement of beans for resistance to insect pests is essential for minimizing yield losses arising from crop damage. The objectives of this study were to (1) assess combining ability for bean fly resistance and seed yield accumulation in common bean and (2) estimate genetic parameters associated with resistance for formulating further breeding strategy. Four parents with known reaction to bean fly were crossed with four locally adapted genotypes in an 8 × 8 half diallel mating design. Parents and F₂ progenies were grown in an alpha-lattice design replicated twice in an open-field and subjected to natural populations of bean fly for two cropping seasons under semi-arid conditions. Similarly, two resistant and two susceptible parents were selected and crossed to produce populations for generation means and variances components analysis. Results revealed that both general combining ability (GCA) and specific combining ability (SCA) mean squares were significant (p ≤ 0.05) for all four traits studied except SCA for stem damage during one cropping season. Among the parents, GBK 047858 was the best general combiner for all the traits studied across seasons except for stem damage during long rains (LR) 2009. Besides, genotypes GBK 047821 and Kat × 69 (a locally adapted variety) were generally good general combiners for resistance traits as well as seed yield. General predictability ratio (GPR) values ranging from 0.63 to 0.90 were obtained for plant mortality, stem damage, pupae in stem and seed yield across cropping seasons. These results established the predominance of additive gene effects (fixable variation) over the non-additive effects in controlling the traits. Low to moderate narrow sense heritability values ranging from 0.22 to 0.45 were obtained for pupae in stem. Such heritability estimates indicate that although additive gene components were critical in the inheritance of resistance for the trait, non-additive gene action were also important in addition to the environmental effects.     

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.     

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.     

Genotype-by-environment interactions for grain yield associated with water availability at flowering in rainfed lowland rice

While a large genotype-by-environment (G × E) interaction component of variance for grain yield (GY) has been widely reported for rainfed lowland rice, the reasons for such large interactions are not well known. A random reference population of 34 genotypes taken from the Cambodian rice improvement program was used to examine the magnitude and nature of G × E interactions for GY in Cambodia. These genotypes were evaluated in a multi-environment trial (MET) conducted across 3 years (2000–2002) and eight locations in the rainfed lowlands. The G × E interaction was partitioned into components attributed to genotype-by-location (G × L), genotype-by-year (G × Y) and genotype-by-location-by-year (G × L × Y) interactions. The G × L × Y interaction was the largest component of variance for GY. The G × L interaction was also significant and comparable in size to the genotypic component (G). The significant G component was partly explained by a group of four genotypes that were broadly adapted to different environmental conditions represented by three environmental groups. The three environmental groups were identified from a pattern analysis, and the grouping was partly related to the time of sowing, and hence water availability at flowering. A major factor contributing to the large G × L × Y interactions for GY was late maturing genotypes being affected greatly when soil water availability at flowering was reduced greatly, compared to earlier maturing genotype groups. While the differential genotypic responses to the water availability environment explained part of a large G × E interaction for GY, other non-water related environmental conditions also appeared to have contributed to the interaction. Three target environments were identified for focusing efforts of the breeding programs in Cambodia, and four putative genotypes were selected for their high yield and wide adaptation in the rainfed lowlands.     

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.     

Evidence of genetic transmission of antibiosis and antixenosis resistance of sorghum to the spotted stemborer, Chilo partellus (Lepidoptera: Pyralidae)

Spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), is the most important pest of sorghum in Asia and south and eastern Africa. Host plant resistance is an important control tactic for controlling this pest. Two breeding lines 27B × PB 15881-3 and 463B × PB 15881-3 with their parents, resistant and susceptible genotypes were evaluated in the field, glasshouse and laboratory for different resistance parameters. Breeding lines and genotypes varied significantly in foliar damage ratings, percentage of stem length tunneled, percentage of plants with deadhearts, larval survival, larval and pupal weights, larval and pupal duration, and percentage pupation and adult emergence in diets amended with leaf powder of different sorghum genotypes. The breeding lines 27B × PB 15881-3 and 463B × PB 15881-3 showed antixenosis and antibiosis to C. partellus in terms of reduced eggs per plant, larval survival and development. The levels of antixenosis and antibiosis of both breeding lines were similar to their resistant parents. Results indicate that transmission of characteristics responsible for resistance to the progeny from the resistant parent occurred.     

Mapping quantitative trait loci (QTLs) associated with dough quality in a soft × hard bread wheat progeny

Bread wheat (Triticum aestivum L.) quality is a key trait for baking industry exigencies and broad consumer preferences. The main goal of this study was to undertake quantitative trait loci (QTL) analyses for bread wheat quality in a set of 79 recombinant inbred lines (RILs) derived from a soft × hard bread wheat cross. Field trials were conducted over two years, utilizing a randomized complete block design. Dough quality was evaluated by sedimentation test, mixograph and alveograph analysis. Protein content was measured by near-infrared reflectance analysis and grain hardness was determined by the single kernel characterization system (SKCS).     

Multi-environment field testing for identification and validation of genetic resistance to Botrytis cinerea causing Botrytis grey mold in chickpea (Cicer arietinum L.)

Botrytis grey mould (BGM), caused by Botrytis cinerea Pers. Ex. Fr., is a destructive foliar disease of chickpea (Cicer arietinum L.) worldwide. Disease management through host-plant resistance is the most effective and economic option to manage this disease. The objective of this study was to identify new sources of resistance to BGM, validate their stability across environments and determine the magnitude of G × E interaction. One hundred and nine chickpea genotypes with moderate levels of resistance (BGM severity ≤5.0 on a 1–9 scale) were selected from the preliminary evaluation of 412 genotypes including germplasm and breeding lines under controlled environmental conditions in 2004–2005 at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India. In order to validate resistance stability, an ‘International Botrytis Grey Mould Nursery’ (IBGMN) was constituted with 25 genotypes and tested in multi-environments for BGM resistance at two locations (Gurdaspur and Pantnagar) in India for 4 years and two locations (Tarahara and Rampur) in Nepal for 3 years. Additive main effects and multiplicative interaction (AMMI) analysis showed significant genotype (G), environment (E) and G × E interaction (p < 0.0001) with largest contribution by environment (47.36%). The first two principal component axes were significant, and contributed 48.21% to the total G × E interaction. The AMMI biplot analysis allowed the selection of five genotypes ICCV 96859, ICCV 96853, ICCV 05604, ICCV 96852 and ICCV 05605 with low BGM severity (between 3.7 and 4.7 on 1–9 scale) and moderate stability. Genotype ICCV 96859 having least disease severity and moderate stability could be highlighted and exploited in chickpea resistance breeding programmes.     

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.     

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.     

Field evaluation of upland rice lines selected for QTLs controlling root traits

A marker-assisted back-cross (MABC) programme was used to introgress four root quantitative trait loci (QTLs) from the tropical japonica rice variety Azucena into the Indian upland rice variety, Kalinga III. Previously we tested the products for root traits and reported that the introgressed QTL9 (on chromosome 9) significantly increased root length in the new genetic background. Here we describe field testing for agronomic traits in near-isogenic lines (NILs) that differ for introgressed QTLs. Four NILs were selected and characterised in replicated field experiments in eastern and western India over 3 years. They were tested by upland farmers in a target population of environments (TPE) in three states of eastern India, over 2 years. NILs out-performed Kalinga III for grain and straw yield and there was interaction between the genotypes and the environment (G × E). No effect was found for the root QTL9 on grain or straw yield, however, the presence of several introgressions significantly improved both traits. Some of this effect was due to introgression of Azucena alleles at non-target regions. Overall, the Azucena introgressions increased straw yield more than grain yield. While it has yet to be demonstrated whether this effect is due to improved root systems, this finding fits with the assumption that introgressed genes are involved in partitioning of biomass to the roots and stems, rather than to the grain. The NILs could replace Kalinga III for cultivation in medium upland environments in eastern India.     

Crop hosts and genotypic resistance influence the biological activity of Bacillus thuringiensis towards Helicoverpa armigera

Studies on the influence of genotypic resistance on biological activity of a commercial formulation of Bacillus thuringiensis (Bt) and pure Bt toxin Cry1Ac were carried out to develop appropriate strategies for pod borer, Helicoverpa armigera management in chickpea, sorghum, pigeonpea and cotton. The interaction effects of host plant resistance and biological activity of commercial Bt/Cry1Ac were studied by incorporating the lyophilized tissues of chickpea leaves, milk stage sorghum grain, pigeonpea pods and cotton squares into the artificial diet with and without Bt formulation or Cry1Ac. The H. armigera larval weights were significantly lower in insects reared on diets with square powder of the insect - resistant Bt-cotton RCH 2 + Bt/Cry1Ac and pod powder of insect - resistant pigeonpea genotype, ICPL 332WR + Bt/Cry1Ac as compared to the larvae reared on diets with leaf powder of H. armigera susceptible chickpea genotype, ICCC 37 and the standard artificial diet. Pupation and adult emergence were significantly lower in insects reared on diets with tissues of pod borer-resistant genotypes + Bt/Cry1Ac as compared to insects reared on diets with tissues of the insect susceptible genotypes + Bt/Cry1Ac. Insects reared on diets containing insect-resistant and -susceptible genotypes of sorghum, pigeonpea and cotton and pod borer-resistant genotype of chickpea (ICC 506EB) + Bt/Cry1Ac did not lay any eggs. However, eggs were laid by the insects reared on diets containing pod borer-susceptible genotype of chickpea, ICCC 37 and on the standard artificial diet + Bt/Cry1Ac. The insects reared on diets with sorghum genotype, ICSV 745, and Bt-cotton, RCH 2 without Bt/Cry1Ac also did not lay eggs. The results suggested that Bt/Cry1Ac is more effective for management of H. armigera when deployed in combination with insect-resistant genotypes of cotton, chickpea, pigeonpea and sorghum.     

Contribution of synthetic tetraploids (AAAA) and diploids (AA) to black Sigatoka resistance and bunch weight to their triploid progenies

The generation of banana triploids from tetraploid-diploid crosses requires knowledge on the influence of the parents on black Sigatoka resistance and agronomic traits to the triploid progenies. The objective of this investigation was to determine the influence of tetraploid and diploid parents on black Sigatoka resistance and agronomic traits in the triploid progenies generated from tetraploid-diploid crosses. The mating scheme was designed as a 4 × 5 North Carolina II mating design. Due to problems in seed set and germination, progenies from 2 male parents with 4 female parents were evaluated at two sites in Uganda. The results showed that the male-parent triploid progeny heritability estimate for the number of leaves at harvest was greater than the female parent estimate. The diploid parents had higher correlation coefficients for the total leaves at harvest with the triploid progenies than tetraploid parents with triploid progenies. Disease development over time took more days in diploid parents than in the tetraploid parents with the triploid progenies as intermediates. These results suggested that diploids transferred black Sigatoka resistance to the triploid progenies as measured by the number of standing leaves and disease development overtime. There was a positive correlation (P < 0.05) between tetraploid female parents and triploid progenies for plant height and bunch weight. The triploid progeny-tetraploid female parent heritability estimates for plant height (0.92) and bunch weight (0.72) were highly significant. These results indicated that the female synthetic tetraploids influenced plant height and bunch weight in the triploid progenies. Therefore, it is important to select the tetraploids with heavy bunches to effectively improve yield in triploid progenies generated by tetraploid-diploid crosses. The tetraploid-diploid progenies had a significant (P < 0.05) family-by-site interaction for bunch weight indicating that new banana genotypes need to be tested across different environments to select stable genotypes to promote to end-users.