J. H. Williams

Evaluation of groundnut genotypes for heat tolerance under field conditions in a Sahelian environment using a simple physiological model for yield

Heat tolerance of groundnut (Arachis hypogaea L.) was evaluated under field conditions using physiological traits identified in a yield model [crop growth rate (C), reproductive duration (Dr) and partitioning (p)]. In 1991, 625 diverse genotypes were initially screened under irrigation during the hottest months (February to May). Subsequent tests consisted of 16 contrasting genotypes selected based on a combination of high pod yield and partitioning coefficient of >0· 50. Large variation was observed among the 625 genotypes for pod yield and physiological traits. C was a powerful factor influencing pod yield. Eight genotypes combining high pod yield and a partitioning coefficient greater than 0·6 were identified. These included two released cultivars (55–437 and 796) in the Sahel. Correlations between seasons were significant for p (r=0·84), but non-significant for pod yield (r=0·40), C (r=0·39), and Dr (0·36). Date of sowing and genotypes had significant effects on pod yield and C, but were slight on p and Dr. Pod yield of most genotypes declined by more than 50% when flowering and pod formation occurred when maximum temperatures averaged 40°C. The results revealed that estimates of p would be a more reliable selection criterion for identification of genotypes tolerant to heat than yield. Further research is suggested to maximize crop growth rate and partitioning of genotypes growing under supra-optimal temperatures.

Assessment of groundnut cultivars for end-of-season drought tolerance in a Sahelian environment

A 2-year study (1990 and 1991) was conducted at the ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) Sahelian Centre, near Niamey, Niger, to select groundnut cultivars tolerant to drought and to examine selection techniques. Thirty-six cultivars known to vary in yield potential were grown under rainfed and irrigated conditions. Crop growth rate (C) and partitioning co-efficient (p) were estimated from phenological and final harvest data. The correlation between years was greater for partitioning than for pod yield (implying a higher heritability for p than for yield). Tolerance as determined by a drought susceptibility index for pod yield (S Y ), crop growth rate (S c ) and partitioning (S P ) to reproductive sinks showed thirteen cultivars as drought tolerant for either C or p or for both. The Sahelian cultivars 796, 55-437 and TS 32-1 were the most consistent for drought tolerance. Partitioning was the most important yield component affecting yield variation among cultivars.

Light interception as a source of variation for nitrogen fixation in groundnut genotypes

A range of groundnut (Arachis hypogaea L.) genotypes, representing the cultivated botanical groups, were grown at ICRISAT Center, India. In 3 experiments, 3–8 genotypes were grown at various plant-population densities. In a fourth experiment, 27 genotypes were grown at a constant spacing. Acetylene reduction (AR) and fractional light interception (f) by these cultivars were measured at several stages of crop growth. Plant population (density), sample date and genotype influenced both the AR rate m-2 and the fraction of light intercepted; variables that were well correlated. In 3 experiments, ca. 90% of the statistical variation in AR rate m-2 was attributed to variations in f. In the remaining experiment, genotypic variance was 46% of the explained variance; one genotype (Gangapuri) had consistently low AR across the range of populations, however in the other experiments Gangapuri did not differ from other cultivars in AR/f, when sampled at earlier stages of development.

Effects of seasonal variation in temperature and cultivar on yield and yield determination of irrigated groundnut ( Arachis hypogaea ) during the dry season in the Sahel of West Africa

In the Sudano-Sahelian zone of West Africa there is potential for groundnut (Arachis hypogaea L.) to be grown as a dry-season crop where irrigation is available. However, there are substantial variations in the temperatures during the post-rainy season that can be expected to in¯uence growth and yield. An experiment at the ICRISAT Sahelian Centre was done in order to study the effect of sowing date on phenology, yield and the processes of yield determination for four groundnut cultivars under irrigation in the dry seasons of 1990}91 and 1991}92. Starting on 15 November, eight sowing dates at 2-weekly intervals were tested. Sowing date signi®cantly affected phenology (time to emergence, ¯owering and maturity) with groundnut sown in November}December taking the longest time to reach these phenological stages. November and December sowings gave the highest pod yield within each year, despite the lowest crop growth rates (B), and yield declined progressively as sowing occurred later (50%decrease by March) despite increasing B. The observed responses appear to have been due to the effect of temperature differences during the pod-®lling phase on partitioning. Partitioning (p) to pods was optimized at c. 30 C, with some indication of cultivar differences in partitioning response to temperature. Across all the environments, cultivars displayed substantial differences in yield stability. When sown late, yields were low and lines with high partitioning were the best. When sown early in the post-rainy season, cultivars with a high B value were the better choices. Plant habit differences and B suggest that radiation interception was a limitation to yield, particularly when the crops were sown in the cool months of the year. However, haulm yield and crop growth rates were not consistently affected by sowing date across the years, and cultivars demonstrated different degrees of stability for B. It is concluded that where pod has a price advantage over fodder, irrigated groundnut for the dry season should be sown in November to allow the crop to develop under the relatively cool temperatures that maximize pod yield. Further agronomic research is suggested to maximize B for individual cultivars for given sowing dates.

The influence of plant growth habit on calcium nutrition of groundnut (Arachis hypogaea L.) pods

In field experiments in India and Niger runner and bunch groundnut cultivars were compared for their pod distribution pattern and its relevance to the calcium (Ca) supply for pod development. Bunch cultivars produced sixty to eighty percent of their pods within 5 cm of the tap root. Runner cultivars explored a radius of up to 30 cm for pod production and exploited the soil area in a more homogeneous manner than bunch types. The available soil volume per pod was 19 to 27 cm3 for bunch types and 43 to 46 cm3 for runner types, varying the potential for Ca competition between pods. Computation of the soil Ca content needed to satisfy pod Ca requirements showed that much higher concentrations were needed for the bunch cultivars than for the runners. No significant differences in Ca content of pods existed between bunch and runner cultivars. However, in the runner cultivars, the Ca content of the more widely dispersed pods in outer zones was greater than that of the more densely populated inner pod zones. Regression analysis of shelling percentage across a range of environments showed that the shelling percentage of runners declined less rapidly than did the shelling percent of bunch types, indicating that runners were more efficient in exploiting Ca at lower soil Ca availability than the bunch types.