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CASE STUDIES


Case W


Beating the drought GenStat


ith this summer’s news from the Horn of Africa, nobody can be unaware of the problems of drought, famine, malnutrition and mortality.


Chickpea is one of several high nutritional value pulses upon which populations in marginal semi- arid areas rely, but it can only provide food if it can grow. Development of drought-resistant strains is important, but this depends on accurate understanding of the factors which underpin it. Chickpeas in drought conditions must grow on


stored moisture in the soil. Deep and dense rooting has long been pursued as the assumed critical factor in exploitation of this and, therefore, in drought resistance. Recent studies of other plants, however, have suggested that this may not necessarily be so. In an experiment with 20 different chickpea genotypes, scientists from the International Crops Research Institute for Semi-Arid Tropics (OCHRIEST), India, and the University of Sydney, Australia, investigated the relative importance of these factors. The plants, selected after field trials for their


drought sensitivity or resistance, were grown in lysimeters under both full irrigation and drought stress conditions, and a range of variables recorded. Analysis of the resulting data in GenStat showed that the conventional assumption was indeed misplaced. Ability to extract water from the soil and survive


is not the only criterion for a food plant. Continued water supply through the later stages when seeds form and fill out is crucial. Paradoxically, it may be that the profuse root systems that have been pursued may actually over extract from the available water reserve, depleting it for the later phase. Varieties demonstrating drought resistance


showed a significantly different pattern of water extraction rates from those which were drought sensitive. They pulled less water in the early, vegetative days, and maintained a lower transpiration rate, leaving more in the soil from which to draw at a higher rate after flowering.


24 Statistics special


in point


From the mapping of herring populations to evaluating a neuroprognostic approach to dyslexia, Felix Grant examines some of the many applications of statistical software


Relationship between seed yield and the pattern of water use at different dates in chickpea genotypes (mean of five replicated plants for each genotype and treatment) grown under water stress during the reproductive stage


From the grower’s viewpoint, weight of yield is an important issue. GenStat showed that the harvested weight was strongly related both to water economy in the fourth and fifth weeks after sowing and, conversely, to rate of water uptake in the seventh to ninth weeks. Between yield weight and either root length and density or dry root weight, on the other hand, regardless of depth, there was no significant correlation. Contrary to previous belief, the single most critical factor associated with drought resistance was the early phase tendency to water economy.


Sources M Zaman-Allah, M Jenkinson, and V Vadez, ‘A conservative pattern of water use, rather than deep or profuse rooting, is critical for the terminal drought tolerance of chickpea’ Journal of Experimental Botany, May 2011.


GenStat: www.vsni. co.uk/software/genstat/


Galayko Sergey/Shutterstock


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