Abstract:

Chilling injury in rice has become a severer problem for hybrid production in China in recent years under global warming.Meanwhile a standard method for chilling tolerance screening in heavypanicle rice has been lacked.Thus this experiment aimed to establish a possible method for chillingtolerance screening of heavypanicle rice varieties.The experiment was conducted with 21 heavypanicle maleparent varieties of hybrid rice in phytotron，with chilling stress treatment at their meiosis stages by simulating the local typical injury meteorological factors.The treatment kept continuous seven days with a daily average temperature 17.5℃,and the spikelet pollination rate (SPR) and the spikelet number per panicle (SNP) were chosen to be the criteria for screening the varieties with or with no tolerance to the chilling stresses.As a result，all the varieties were classified into four groups by their tolerances，the tolerant，moderate tolerant，moderate susceptible and the susceptible.Among them,BL006，RHQ and Xiangba belonged to be the tolerant group，and C418 the susceptible.After the chilling stress treatment，in comparison with the controls，the tolerant varieties showed higher SPRs and SNPs，with no change in anther length (AL)，the pollinated pollens per stigma(PPS)，the germinated pollens per stigma(GPS)，and the pollen germination rate per stigma(PGRS).On the contrary，C418 demonstrated sharp decreases in their SPRs and SNPs，anther length，the pollination pollens per stigma，the germination pollens per stigma，and the pollen germination rate per stigma after their treatments.The result showed that different from the normal panicle type rice variety，the heavypanicle rice variety susceptible to chilling stress tended to reduce its spikelet formation.While as the same as the normal panicle rice variety，its male microgamete tended to be deteriorated in structure and functioning under chilling stress process.Thus a joint screening indicator with SPR plus SNP，not just SPR，may be necessary for chillingtolerance screening in heavypanicle rice variety.We concluded that the chilling tolerance of heavypanicle rice variety can be screened with joint criteria of SPR plus SNP under simulation conditions based on the local typical injury meteorological factors.Moreover，under chilling conditions，in comparison with the tolerant ones，susceptible varieties showed apparent decreases in their SPRs，and deterioration in their pollen quantities and qualities as well