Temperature-stratified screening of chickpea ( Cicer arietinum L.) genetic resource collections reveals very limited reproductive chilling tolerance compared to its annual wild relatives

Abstract

Low reproductive chilling tolerance in chickpea impairs ovule fertilization, delaying pod set, exposing the crop to terminal drought throughout much of its distribution range. Despite this realization, little progress has been made because of the limited genetic variation available to breeders. To address this issue a wide range of domesticated ( n = 1762) and wild Cicer ( n = 200) germplasm collected from sites stratified by flowering phase temperature was extensively field evaluated, and compared with Lupinus angustifolius, a well-adapted Mediterranean winter annual. Chilling tolerance was estimated by regressing the time interval between pod set and first flower against mean post-anthesis temperature. Field screening was augmented by smaller scale experiments evaluating the effects of contrasting post-anthesis temperature regimes on plant growth and productivity, pollen function and subsequent pod set in temperature-controlled cabinets. Chickpea was less chilling tolerant than its wild relatives, the flower-pod interval increasing curvi-linearly as sites became cooler, with a strong effects between 11 and 16 °C, tailing off after 17.5 °C, but remaining statistically significant. There is little useful variation for chilling tolerance within domesticated chickpea. Small, albeit statistically significant differences in pod set delay in chickpea collected from contrasting flowering phase habitats, were marginal compared to more tolerant species such as Cicer bijugum, Cicer judaicum and L. angustifolius, and to a lesser extent Cicer reticulatum, Cicer pinnatifidum, and Cicer echinospermum. No differences were observed between desi and kabuli types. Field screening identified robust chilling tolerance in a C. echinospermum accession that commenced podding earlier, at lower temperatures (10.0 °C), and yielded 5 times more than Rupali, the most productive chickpea. Controlled temperature experiments confirmed that in contrast to chickpea, pollen germination, viability, frequency on the stigma surface and subsequent pod set were unaffected by low post-anthesis temperatures (13/7 °C) in C. echinospermum and L. angustifolius. Our results indicate that chickpea is even more chilling sensitive than previously thought. Because C. echinospermum is inter-fertile with chickpea, it has considerable potential both as a donor of robust chilling tolerance and as an agent for investigating resistance mechanisms.