All India Coordinated Rice Improvement Project, Rajendranagar, Hyderabad-500030, India
Twenty three medium duration pre-release cultures, 97 cultures from Kashmir during rabi 1975, and 42 cultures comprising Kashmir material and Basmati-370, H-4, Sona, Bhavani, RP 4-14 and Mahsuri during rabi 1976, were assessed in dry hot summer season for their occurrence of sterility and ripening under field conditions. A majority of the cultures flowered between the last week of March and the first week of April and the ripening prolonged upto May in certain cases. During this period, a triple factor combination of high temperatures-How humidity+high solar radiation was recorded. There was varietal variation for both unfertilized spikelets (sterility) and grain filling (ripening); and under Hyderabad conditions, pain filling appeared to be the major problem. Although high temperatures can cause sterility and impair ripening, the role of the triple factor syndrome was considered more important. In view of very low grain filling percentage recorded in several varieties, the percentage of ripened grains needs consideration while developing new varieties meant for summer cultivation.
