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.     

Distribution of seed protein fractions and amino acids in different anatomical parts of chickpea (Cicer arietinum L.) and pigeonpea (Cajanus cajan L.)

Studies on protein fractionation in seed coat, embryo, cotyledons and whole seed were made to observe the differences, if any, between chickpea and pigeonpea. Results indicated that globulin was the major fraction of embryo and cotyledons of these legumes. Seed-coat nitrogen was observed to be mostly comprised of nonprotein nitrogen and glutelin fractions and thus differed from other components in both chickpea and pigeonpea. The albumin fraction of cotyledons of both crops had the highest concentration of sulphur amino acids, methionine and cystine. Glutelin contained a considerably higher concentration of methionine and cystine than did globulin in chickpea and pigeonpea. This suggests that lines with higher glutelin should be identified to improve their protein quality. The amino acid compositions of different seed components did not show large differences between these two pulse crops.Submitted as JA no. 180 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).     

Influence of the soil physical environment on rice (Oryza sativa L.) response to drought stress and its implications for drought research

Plant performance under drought stress is not solely defined by an inadequate water supply but by an interaction among many factors, including climatic, edaphic, and biological factors. An important interacting factor affecting root growth, and therefore the ability of a plant to access and take up water, is the soil physical environment. Soil penetration resistance can restrict, or even halt, root system growth. For rice, a soil penetration resistance of 1.4 MPa is sufficient to inhibit root system expansion. This review describes the effects of the soil physical environment on root growth and its interaction with drought stress. A large variation in soil penetration resistance exists among rainfed rice-growing areas of South and Southeast Asia and within experimental stations used for managed-drought field phenotyping. This variability may influence genotypic performance across experimental sites/countries and the response of crop genotypes to drought stress. A case study is presented in which differences in the soil physical environment may partially elucidate differences in experimental results between two field studies conducted at different locations. These results highlight the need for increased knowledge of environmental interactions to allow the outputs of genomics to increase drought tolerance at the field level.     

Selection for resistance to Phytophthora pod rot of cocoa (Theobroma cacao L.) in Cameroon: Repeatability and reliability of screening tests and field observations

Phytophthora pod rot (Ppr) disease caused by Phytophthora megakarya is the major constraint to cocoa production in Cameroon. The development of resistant varieties requires the use of effective resistance testing methods. The repeatability and reliability of the leaf disc and detached pod tests, as applied in selection activities in Cameroon, were studied. Repeatability of the tests was estimated by calculating the correlation (r) between resistance scores of clones, progenies and individuals within progenies in different inoculations rounds of the leaf disc and detached pod tests. Such correlations were generally significant for both tests. For the leaf disc test, as expected, correlations were lower for individuals within seedling progenies than for the average of seedling progenies or of clones. This suggests that a higher number of replicate observations are required for correct evaluation of individual seedlings than for evaluation of the average level of resistance of progenies. Observations carried out 5 or 7 days after inoculation was highly correlated, suggesting that scoring in the leaf disc test may be done only once at 5, 6 or 7 days after inoculation. In one experiment the ranking of leaf disc and detached pod inoculation test results could be compared statistically, with data being significantly correlated (r 0.78). The reliability of the tests was evaluated by the correlations between results of the tests and the level of field infection. These were generally positive and significant, for the leaf disc and detached pod test. A variation between mean scores of 5 and 8 in the detached pod test appeared to be related to a 40% difference in field infection with P. megakarya in years with medium disease pressure. However, correlations with field resistance were not always significant, suggesting the influence of uncontrolled environmental factors affecting field observations or the results in the screening tests. It is concluded that the leaf disc and detached pod tests, if applied under standardized conditions, can be of great value to speed up selection for Ppr resistance.