Heritability of,and genotypic correlations between,aflatoxin traits and physiological traits for drought tolerance under end of season drought in peanut (Arachis hypogaea L.)

More rapid progress in breeding peanut for reduced aflatoxin contamination should be achievable with a better understanding of the inheritance of, aflatoxin trait and physiological traits that are associated with reduced contamination. The objectives of this study were to estimate the heritability of aflatoxin traits and genotypic (r_G) and phenotypic (r_P) correlations between drought resistance traits and aflatoxin traits in peanut. One hundred-forty peanut lines in the F_4:6 and F_4:7 generations were generated from four crosses, and tested under well-watered and terminal drought conditions. Field experiments were conducted under the dry seasons 2006/2007 and 2007/2008. Data were recorded for biomass (BIO), pod yield (PY), drought tolerance traits [harvest index (HI), drought tolerance index (DTI) of BIO and PY, specific leaf area (SLA), and SPAD chlorophyll meter reading (SCMR)], and aflatoxin traits [seed infection and aflatoxin contamination]. Heritabilities of A. flavus infection and aflatoxin contamination in this study were low to moderate. The heritabilities for seed infection and aflatoxin contamination ranged from 0.48 to 0.58 and 0.24 to 0.68, respectively. Significant correlations between aflatoxin traits and DTI (PY), DTI (BIO), HI, biomass and pod yield under terminal drought conditions were found (r_P = −0.25** to 0.32**, r_G = −0.57** to 0.53**). Strong correlations between SLA and SCMR with A. flavus infection and aflatoxin contamination were also found. Positive correlations between SLA at 80, 90, and 100 DAP and aflatoxin traits were significant (r_P = 0.13** to 0.46**, r_G = 0.26** to 0.81**). SCMR was negatively correlated with aflatoxin traits (r_P = −0.10** to −0.40**, r_G = −0.11** to −0.66**). These results indicated that physiological-based selection approaches using SLA and SCMR might be effective for improving aflatoxin resistance in peanut.     

Combining ability analysis for Phaeosphaeria leaf spot resistance and grain yield in tropical advanced maize inbred lines

Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Renfro) of maize is increasing in importance in sub-Saharan Africa (SSA). However, there is still limited information on the combining ability for disease resistance of the germplasm that are adapted to African environments. Evaluating combining ability effects and their interactions with the environment would provide valuable information that can be used in the development of cultivars that are resistant to PLS. This study was therefore conducted to determine the combining ability, gene action and the relationship between grain yield and PLS disease severity among selected tropical advanced maize inbred lines. Forty five F₁ hybrids were generated by crossing 10 inbred lines in a half diallel mating scheme. The 45 hybrids along with the ten inbred parents were evaluated in four environments, with two replications each between 2007 and 2009. General and specific combining ability (GCA and SCA) effects were highly significant (P ≤ 0.001) for PLS, grain yield and days to anthesis. GCA effects accounted for 66–90% and SCA effects for 10–34% of the variation in the hybrids for PLS resistance, grain yield and days to anthesis. This indicated predominance of additive over non-additive gene action for the three traits in these inbred lines. The resistant inbred lines to PLS were A1220-4, N3-2-3-3, CML312, MP18 and CML488. These lines had good combining ability for PLS resistance and contributed towards resistance in their crosses. In general, resistant hybrids involved a susceptible and a resistant parent, where at least one of the parents had a negative GCA effect. In addition, lines A1220-4 and CML312 contributed towards high yield and were late maturing. Inbred line CZL00009 conferred genes for early maturity. Linear regression analysis indicated that grain yield of maize was suppressed by about 250 kg ha⁻¹ per each increase in PLS disease severity score, underscoring the need to control the disease. Significant (P < 0.01), negative correlations (r = −0.29 to −0.43) between grain yield and PLS severity were also detected. This showed the potential of PLS to reduce yield when favourable conditions for disease development are present. By and large, highly significant additive gene action implied that progress would be made through selection. Although non-additive effects were small (±10%), observation of dominance effects which were associated with reduced disease levels in some hybrids may be exploited in developing single cross maize hybrids among these inbreds when one parent is resistant.     

Transgressive variants for red pericarp grain with high yield potential derived from Oryza rufipogon × Oryza sativa: Field evaluation, screening for blast disease, QTL validation and background marker analysis for agronomic traits

Five transgressive variants (advanced breeding lines from BC₂F₅ and BC₂F₆ generation) were derived from a cross between the wild relative, O. rufipogon Griff. and O. sativa L. subsp. indica cv. MR219, a popular high yielding Malaysian rice cultivar. The aim of the study was to evaluate the pericarp colour of the grains along with yield potential and to validate quantitative trait loci (QTLs) for agronomic traits. The variants were screened against blast disease. Background marker analysis was also done for the promising variants. The field trials were carried out at a single location (due to containment purposes) over two seasons using randomized complete block design (RCBD) with three replications. A trait-based marker analysis was used to identify QTLs for validation in BC₂F₅ generation. Analysis of variance (ANOVA) showed that the seasonal factors influenced different agronomic traits. Variant G33 produced significantly (p < 0.05) higher yield (5.20 t/ha) than the control, MR219 (4.53 t/ha). Eighteen QTLs for different agronomic traits were identified in BC₂F₂ population in a previous study. Among them 14 QTLs were found in BC₂F₅ population of the present study. The yield of variant G33 was influenced by several QTLs viz. qGPL-1, qSPL-1-2, qSPL-8 and qYLD-4, which were introgressed from the donor parent revealed by background marker analysis using BC₂F₇ generation. Percentage (99%) of red pericarp grain of G33 and G34 in BC₂F₅ and BC₂F₆ generations indicated the stability of pericarp colour which was transferred from the wild relative. Variant G33 showed resistance against two pathotype of blast disease (Magnaporthe oryzae). Among the evaluated variants, G33 could be considered for inclusion in the cultivar development program for red rice with high yield potential and resistance to blast disease. This study demonstrated that the alleles from wild relative could improve the yield and yield related traits through allelic interaction, even though the phenotypic traits were inferior to the recurrent parent.     

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.     

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.     

Quantification of yield loss due to coffee leaf scorch

Coffee leaf scorch caused by Xylella fastidiosa is widespread in major coffee-growing regions of Brazil. This study was done to quantify the yield loss caused by this disease. The severity data of the disease were collected during the 2006, 2007 and 2008 seasons at commercial plantations growing Coffea arabica ‘Catuaí’ in São Gotardo-MG in 250 plants of three blocks of 7000 coffee plants each. Fifty selected plants per block with different disease severities were determined. The linear regression showed a significant relationship (P < 0.01) between disease severity and bean yield and between disease severity and grain size in all years. The relationship between yield and the disease severity was significant (P < 0.01). For each 1% increase in the disease severity, there was a decrease of 1.22, 1.34 and 2.02 bags of bean yield/ha in 2006, 2007 and 2008, respectively, thus showing the importance of the disease in reducing coffee bean yields.     

Toxicity of quinones against two-spotted spider mite and three species of aphids in laboratory and greenhouse conditions

Toxicities of the eight quinones were evaluated through leaf dip bioassays conducted against Tetranychus urticae, Myzus persicae, Myzocallis walshii, and Illinoia liriodendri. Based on LC₅₀ values, plumbagin (LC₅₀ = 0.001%) was the most active compound against T. urticae and ubiquinone Q₀ (LC₅₀ = 0.005%), plumbagin (LC₅₀ = 0.010%), and dibromothymoquinone (LC₅₀ = 0.012%) were the most active compounds against M. persicae. The most active compounds against M. walshii were juglone (LC₅₀ = 0.011%) and ubiquinone Q₀ (LC₅₀ = 0.019%), whereas dibromothymoquinone (LC₅₀ = 0.030%), plumbagin (LC₅₀ = 0.033%) and ubiquinone Q₀ (LC₅₀ = 0.058%) were the most toxic to I. liriodendri. Ecotrol (positive control) was the least toxic compound (LC₅₀ = 0.39%) against T. urticae and M. persicae (LC₅₀ = 0.447%). Although the majority of the compounds tested were toxic to all four test species in residual bioassays, there was little overlap among the test species in terms of susceptibility to the compounds and interspecific differences were observed. Regarding structure-activity relationships for quinones, the addition of a hydroxyl group resulted in a significant increase in the toxicity of the 1,4-naphthoquinones, and those possessing a methyl group exhibited the highest levels of activity in T. urticae. The bromine atom at the 2- and 5-positions of the benzoquinone ring is crucial to the toxicity of the compounds against I. liriodendri. Toxicity was greatly affected not only by the number of hydroxyl groups, but also by their positions in the ring in the case of M. walshii. Juglone and plumbagin as residual toxins in the laboratory also reduced the population of two-spotted spider mites compared to EcoTrol™ (positive control) and the negative control in the greenhouse experiment. Some quinones tested may have potential as commercial insecticides and miticides, or alternatively, could serve as lead compounds for the development of more potent crop protection agents.     

Repellent effects of five monoterpenoid odours against Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) in Calabar, Nigeria

Secondary plant compounds are recognised as important components of plant defence system against herbivores and pathogens. Five monoterpenoids, (R)-linalool, 1,8-cineole, (S)-2-heptyl acetate, (S)-2-heptanol and citral, which are natural components of the essential oils of Aframomum melegueta (K. Schum) and Zingiber officinale (Roscoe), were tested at the ratios in which they occur naturally for repellent activity against Tribolium castaneum (Herbst.) and Rhyzopertha dominica (F.) in a 4-way olfactometer. The results showed the repellent properties of the compounds as both beetles spent less time in the olfactometer arm containing the test stimuli. (R)-linalool and (S)-2-heptanol were stronger repellent compounds than the others. Linalool showed good repellent activity against T. castaneum (P = 0.001) as the insect spent 1.22 min in the test arm compared to the control arms (2.78 min), and R. dominica (P = 0.001) with 0.89 min in the test arm compared to 2.87 min in the control arms. With (S)-2-heptanol, T. castaneum spent 1.23 min in the test arm compared to 2.83 min in the control arms. R. dominica spent 1.61 min in the test arm and 2.69 min in the control arms. For the number of entries or visits made, while both insects were significantly repelled (P < 0.05) by the linalool-treated arm than the control, only R. dominica was repelled by the (S)-2-heptanol-treated arm (P = 0.038) compared to the control arms. The results indicate that A. melegueta and Z. officinale essential oils and their components could be suitable as safer repellents or fumigants against T. castaneum and R. dominica.     

Effects of crude seed extracts of Annona atemoya and Annona squamosa L. against the cabbage looper, Trichoplusia ni in the laboratory and greenhouse

Antifeedant, growth inhibitory and toxic effects of crude seed extracts of Annona squamosa and Annona atemoya from Fazenda Viveiro Bona, Parasisópolis – Minas Gerais, Brazil, were evaluated against the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) using different bioassays. Crude methanolic seed extracts deterred feeding of third instar T. ni larvae in a leaf disc choice bioassay. A. squamosa was ∼10 times more active as a feeding deterrent than A. atemoya (DC₅₀ = 2.3 mg/ml vs. 20.1 mg/ml). A. squamosa was ∼three times more active as a growth inhibitor than A. atemoya (EC₅₀ = 38.0 ppm vs. 117.0 ppm). Methanolic seed extracts of A. squamosa and A. atemoya were toxic to third instar T. ni larvae both through topical and oral application. A. squamosa was more toxic through feeding (LC₅₀ = 167.5 ppm vs. 382.4 ppm) whereas, A. atemoya exerted greater toxicity via topical application (LC₅₀ = 301.3 μg/larva vs. 197.7 μg/larva). Both A. squamosa and A. atemoya extracts reduced leaf area consumption and larval growth in a greenhouse experiment. Our results indicate that both A. squamosa and A. atemoya have potential for development as botanical insecticides, especially for local use in Brazil.     

Environmental effects on seed yield determination of irrigated peanut crops: Links with radiation use efficiency and crop growth rate

In Argentina, delayed sowing causes a decrease in seed yield and in radiation use efficiency (RUE) of peanut crops (Arachis hypogaea L.), but it is not known if RUE reduction is mainly due to reduced temperature during late reproductive stages or to a sink limitation promoted by decreased seed number in these conditions. We analyzed seed yield determination and RUE dynamics of two cultivars (Florman and ASEM) in four irrigated field experiments (Exp_n) grown at three sites and five contrasting sowing dates (between 17 October and 21 December) in three growing seasons. An additional field experiment was performed with widely spaced plants (i.e. with no interference among them) to evaluate the effect of peg removal on RUE and leaf carbon exchange rate (CER). Seasonal dynamics of mean air temperature and irradiance, biomass production (total and pods), and intercepted photosynthetically active radiation (IPAR) were followed. Seed yield and seed yield components (pod number, seeds per pod, seed number and seed weight) were determined at final harvest. Crop growth rate (CGR) and pod growth rate (PGR) were computed for growth phases of interest. RUE values for crops sown until 14 November were 1.89–1.98 g MJ⁻¹ IPAR, within the usual range. RUE decreased significantly for cv. Florman in the late sowing of Exp₁ (29 November) and for both cultivars in Exp₃ (21 December sowing). Across experiments, seed yield (4.5-fold variation relative to minimum) was strongly associated (r² = 0.87, P < 0.0001) with variations in seed number (3.5-fold variation relative to minimum), and to a lesser extent (r² ≤ 0.54, P ≤ 0.001) to variations in seed weight (1.9-fold variation relative to minimum). Seed number was positively related (P < 0.01) to CGR (r² = 0.66) and to PGR (r² = 0.72) during the R₃–R_6.5 phase (seed number determination window), while crop growth during the grain-filling phase (i.e. between R_6.5 and final harvest) was positively associated with grain number (r² = 0.80, P < 0.001). No association was found between RUE and mean air temperature, neither for the whole cycle nor for the phase between R_6.5 and final harvest, which showed the largest temperature variation (16.4–22.4 °C) across experiments. Use of mean minimum temperature records (range between 13.8 and 18.5 °C) did no improve the relationship. However, grain-filling phase RUE showed a positive (r² = 0.69, P = 0.003) linear response to seed number across experiments. This apparent sink limitation of source activity was consistent with the reduced RUE (from 2.73 to 1.42 g MJ⁻¹ IPAR) and reduced leaf CER at high irradiance (from ca. 30 to 15 μmol m⁻² s⁻¹) for plants subjected to 75% peg removal.     

Screening of three sweet potato (Ipomoea batatas L.) cultivars for resistance to different virulence groups of root-knot nematodes (Meloidogyne spp.) under controlled conditions

The susceptibility of three sweet potato cultivars (Ipomoea batatas L.) C4, TIS 3290 and TIS 9162 was evaluated against 156 isolates of Meloidogyne spp. with the aim to include resistant/tolerant sweet potato cultivars in a crop rotation scheme for the management of root-knot nematodes. The nematode isolates corresponded to races 1, 2 and 3 of Meloidogyne arenaria (n = 7), races 1, 2, 3 and 4 of M. incognita (n = 131) and Meloidogyne javanica (n = 18). Also, the isolates of M. incognita were differentiated in virulence groups: Pepper (n = 35), Pepper-Mi (n = 25), Tomato (n = 41) and Tomato-Mi (n = 30), depending on their ability to parasitize resistant pepper and tomato cultivars. The tested isolates of M. javanica parasitized C4 and TIS 3290, but not TIS 9162, whereas M. arenaria parasitized C4 and TIS 9162, but not TIS 3290, and M. incognita was able to parasitize the three sweet potato cultivars tested. C4 was the most susceptible cultivar to all nematode species tested, especially M. incognita, TIS 3290 was the most resistant and TIS 9162 was in between (7.2, 62.9 and 26.9% of resistant plants, respectively). Susceptibility of the sweet potato cultivars showed slight variations depending on the race or virulence group of M. incognita. The results suggest that sweet potato cultivars TIS 3290 and TIS 9162 may be used as rotation crops in fields where root-knot nematodes are present, their selection depending on the Meloidogyne isolates present. The use of resistant sweet potato cultivars would be preferably combined with other management practices to avoid virulence selection in nematode isolates.     

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.     

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.     

Effects of leaf scales of different pineapple cultivars on the epiphytic stage of Fusarium guttiforme

The fungus Fusarium guttiforme (Syn. F. subglutinans f. sp. ananas) is responsible for fusariosis, one of the main phytosanitary threats to pineapple (Ananas comosus var. comosus). A structural study comparing epidermal differences in pineapple cultivars resistant and susceptible to fusariosis was performed, relating properties of the epidermis to known susceptibility to the disease. The basal, non-chlorophylled, portions of mature leaves of pineapple plants were analyzed by light and electron microscopy. All cultivars showed common morpho-anatomic aspects characteristic of Bromeliaceae, such as scutiform scales and unstratified epidermis. However, cultivar Vitoria (resistant) had less scales than cultivars Smooth Cayenne (susceptible, intermediate severity) and Perola (susceptible, with extreme severity of fusariosis symptoms). Inoculation of conidia suspension (10⁵ conidia ml⁻¹) of the fungus F. guttiforme to leaves and harvesting 24 h later yielded numbers of viable colonies related to the density of leaf scales. This suggests that scales can act as havens for fungal conidia and favour the epiphytic stage of the fungus on pineapple plants, and are involved in the interaction of plant and pathogen. A reduction in scale numbers was related to lower infection levels and is relevant to the future breeding programme for development of new pineapple cultivars resistant to fusariosis and their involvement in integrated control strategies.     

Perennial O. sativa × O. rufipogon interspecific hybrids: I. Photosynthetic characteristics and their inheritance

A survey of 24 wild Oryza accessions identified Oryza australiensis and Oryza rufipogon as potential sources of enhanced photosynthetic rate for introgression into cultivated rice. Photosynthetic capacity per unit leaf area (CER) was associated with leaf N content but not with leaf chlorophyll concentration, flag leaf area, or specific leaf area. Eight fertile, perennial F₁ hybrids between O. sativa and O. rufipogon were grown in non-flooded soil, and CER was measured at flowering under saturating light. Two F₁ hybrids had greater CER than the average of 26.1 μmol m² s⁻¹. The F₂ progeny from these hybrids were screened for CER in the field, and segregants with even greater rates of photosynthesis were selected. The basis of high photosynthetic rate in the F₂ populations was not leaf thickness or leaf chlorophyll content. One F₂ line had exceptionally high CER and stomatal conductance. Broad-sense heritability on an individual plant basis for CER in two F₂ populations was 0.44 and 0.37. A highly significant offspring-parent regression of 0.89 for CER was observed in a replicated field evaluation (four blocks, five plants per plot) of 20 vegetatively propagated F₂ selections and their F₃ seedling progeny. Broad-sense heritability for CER on a plot-mean basis was estimated as 0.74 for both selected F_2:3 families and for the selected F₂ clones. Genetic resources in the genus Oryza may represent a source of alleles to increase leaf photosynthetic rate in the cultivated species, which we have demonstrated to be a heritable, though environmentally variable, trait in an O. sativa/O. rufipogon population.     

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.     

Swiss Flint maize landraces—A rich pool of variability for early vigour in cool environments

Today's modern Dent × Flint maize (Zea mays L. ssp. mays) hybrids have a high yield potential but often lack satisfying early vigour under typical low spring temperatures of temperate latitudes. Maize was introduced into Europe already in the 16th century and until the 1950s, landraces evolved and adapted well to various geographically restricted and climatically marginal regions in Europe. Therefore, the objective of this study was to assess representatives of the large pool of Swiss Flint maize landraces for their early vigour under cool conditions in the field. A set of 17 landrace accessions were tested for 2 years at sites on the Swiss plateau (450 and 550 m a.s.l.) and in the foothills of the Swiss Alps (830 and 870 m a.s.l.). Plant emergence (PE), emergence index (EI), the efficiency of the photosystem II (F_v/F_m), leaf greenness (SPAD) and plant dry weight at the three- and six-leaf stages (DW3_P, DW6_P) were measured.     

Activities of essential oils from Asarum heterotropoides var. mandshuricum against five phytopathogens

Some secondary metabolites of plants function as antimicrobial products against phytopathogens and constitute an increasingly important class of pesticides. In the present study, the essential oil of Asarum heterotropoides var. mandshuricum was analyzed by GC/MS and its antimicrobial activity was evaluated against five phytopathogenic fungi. Major components of the oil were methyleugenol (59.42%), eucarvone (24.10%), 5-allyl-1,2,3-trimethoxybenzene (5.72%), and 3,7,7-trimethylbicyclo(4.1.0)hept-3-ene (4.93%). The essential oil and the most abundant component, methyleugenol, were separately assayed for inhibition of 5 pathogens: Alternaria humicola, Colletotrichum gloeosporioides, Rhizoctonia solani, Phytophthora cactorum and Fusarium solani. Both the oil and methyleugenol strongly inhibited the growth of the test pathogens (IC₅₀ values <0.42 μg ml⁻¹) except F. solani, with the best activity against P. cactorum (IC₅₀ values = 0.073 and 0.052 μg ml⁻¹, respectively). It is concluded that the essential oil of A. heterotropoides var. mandshuricum has a broad antiphytopathogenic spectrum, and that methyleugenol is largely responsible for the bioactivity of the oil. The mode of action of methyleugenol against P. cactorum is discussed based on changes in the mycelial ultrastructure.     

Comparative assessment of the field-susceptibility of Sesamia nonagrioides to the Cry1Ab toxin in areas with different adoption rates of Bt maize and in Bt-free areas

A three year (2003-2005) field study compared the susceptibility to the Cry1Ab toxin, expressed in Bt maize, of Mediterranean corn borer (MCB) Sesamia nonagrioides populations collected from areas with different adoption rates of Bt maize in Spain with Bt-free areas in Greece. Spain is the only European country where the cultivar Compa CB derived from the event Bt176 was commercially grown, from 1998 to 2005. The large decrease of the titer of the toxin in this cultivar at later growth stages represented the worst-case scenario for resistance development of MCB, since larvae of the second and third generations were exposed to sublethal concentrations of Cry1Ab toxin. Our data revealed that the variation in susceptibility to Cry1Ab for the MCB Spanish field populations analyzed in the three years was very low, with LC₅₀ values fluctuating between 12 and 30 ng Cry1Ab/cm², regardless of the region of origin, the type of maize (Bt or non-Bt) and the year. Furthermore, no significant differences were found when comparisons were made with a laboratory population (LC₅₀ values: 18-26 ng Cry1Ab/cm²) or with field populations from Greece (Bt-free areas), which displayed LC₅₀ values ranging between 22 and 27 ng Cry1Ab/cm². Standardizing bioassay protocols proved to be essential for obtaining comparable results. These findings suggest that resistant MCB populations did not evolve in those Spanish maize areas where Compa CB was largely cultivated for eight years, contradicting the expected rapid development of resistance under these unfavourable conditions. Additionally, our results can be used as baseline indices in post-market resistance monitoring programs if Bt maize is introduced in Greece. Further studies should continue, since the insights gained from a resistance monitoring program may help to enhance the durability of Bt maize.     

Influence of leaf position that correspond to whole plant severity and diagrammatic scale for white spot of corn

The main objective of this research is to determine the influence of leaf position on corn plants with white spot caused by Pantoea ananatis, which better represents the infection on the whole plant. A diagrammatic scale to quantify the severity of the disease was elaborated and validated. For scale elaboration, the minimal and maximal limits of the disease severity observed in the field were considered, and intermediate levels followed logarithmic increments according to the Weber–Fechner stimulation law. The scale has nine classes: 0.1, 1, 2, 4, 8, 16, 24, 32 and 64%. For scale evaluation, a severity evaluation for white spot was performed by 10 raters with no experience in disease evaluation. Initially, severity estimation was performed without a scale for 41 leaves with different levels of severity. Afterward, the same raters used the proposed diagrammatic scale. Through linear regression to compare the actual and estimate severity values, the raters’ accuracy and precision were analyzed. Satisfactory accuracy and precision were achieved when estimation was performed with a diagrammatic scale. To determine the best leaf disease severity evaluation, correlation and regression analyses were performed with 25 plants of five genotypes, for a total of 284 leaves analyzed. Results analysis leads us to conclude that the severity of white spot on corn plants significantly correlates with the disease mean severity of leaves 0 and -1, i.e., a leaf of the corn ear and the one immediately below it. This scale provided good levels of accuracy and precision (a mean R² of 94%), with errors concentrating around 10%. Raters presented increased reproducibility (R² > 90% in 82% of cases) of severity estimates. The proposed diagrammatic scale is considered adequate to estimate the severity of white spot in corn for germplasm evaluations, for epidemiological studies and for evaluation of control strategies for this disease.