RESPONSES OF YOUNG TEA (CAMELLIA-SINENSIS) CLONES TO DROUGHT AND TEMPERATURE .1. YIELD AND YIELD DISTRIBUTION

The yield response to drought and temperature of six contrasting tea c lones was studied in a line-source irrigation experiment in Southern T anzania. The selected clones, all commercially and/or scientifically i mportant in eastern Africa, embrace a range of morphological and physi ological types. The bushes were planted in August 1988 and differentia l drought treatments were imposed for 16 and 13 weeks towards the end of the dry seasons in 1990 and 1991, respectively. The resulting soil water deficits were successfully simulated using a water balance model . Under well-watered conditions Clone S15/10 (from Kenya) gave the hig hest yield of dry tea, reaching 5600 kg ha(-1) in the fourth year afte r planting (1991/92) compared with 3640-4420 kg ha(-1) for the other f ive clones. During the cool season Clone SFS150 (from Malawi) yielded more than Clones 1, 207, 6/8 and K35. Although annual yields decreased curvi-linearly as the maximum soil water deficit increased, single Va lues for the drought sensitivity of each clone could be derived by usi ng stress time as an index of drought. On this basis Clones S15/10 and 207 were identified as being the most sensitive to drought; Clones SF S150 and 1 were drought resistant. The reasons for these differences i n yield responses and the importance of determining drought sensitivit y over an appropriate time period are discussed.