Genetic adaptation of crop plants to low-nutrient environments: morphological and ecophysiological characteristics of adaptation

Abstract

One hundred genotypes each of sorghum and pigeonpea were screened for their adaptation to soils low in nitrogen (N) and phosphorus (P) on an Alfisol and a Vertisol. The tested genotypes were classified by growth duration, growing habit, plant shape, germplasm collection site, and end use, and results were analyzed by classified groups. A wide range of genetic variation in grain and dry matter yields was observed. Dry matter yield depended on growth duration. For sorghum to attain maximum dry matter yield, growth duration should exceed 80 days, and to attain the maximum growth rate, a main stem longer than 250 cm, large and thin leaves (mean leaf area over 320 cm², specific leaf area (SLA) larger than 250 cm² g), and a leaf/stem weight ratio below 0.6 are required. Total accumulated plant N was positively correlated to dry matter yield but not to N-use efficiency of accumulated N. Results suggest that the ability of roots to absorb soil-N was comparatively more important for biomass productivity under low-N conditions than N-use efficiency. Biomass production in the growth stage and at harvest were not positively correlated, because some hybrids and forage varieties grew vigorously in the late growth stage. This suggests that improvement of growth activities in both early- and late-maturing types should be integrated when breeding for adaptation to low-N soils. Such morphological characteristics as large thin leaves, long main stems, and low leaf/stem weight are required for future ideotypes of sorghum and pigeonpea adapted to low-N and low-P conditions.