A study on heat tolerance in sweet pepper was conducted at the Asian Vegetable Research and Development Centre (AVRDC), Taiwan from December 1999 to May 2000. Experiments were carried out to investigate the influence of 29/23°C and 24/18°C stress on 12 sweet pepper genotypes on growth, development, reproductive behaviour and yield potentialities and to verify the results of the phytotron study. Performance of 12 sweet pepper genotypes was evaluated under two different temperature regimes of 24/18° C and 29/23° C in the phytotron. Plant height was found higher at 29/23° C compared to 24/18° C. High temperature reduced percent fruit set as well as size of fruits. Individual fruit weight was higher (7.44-125.00 g) when grown at 24/18°C and lower (5.35-103.80 g) at 29/23°C. Out of 12 genotypes, SP00l, SP002, SP004, and SP012 performed poor in respect of per plant yield at higher temperature compared to the lower temperature. So, these four genotypes were considered to be heat sensitive than the others. Leaf proline content of the sensitive genotypes decreased under the high temperature conditions and the heat tolerant lines produced higher amount of proline indicating the role of proline in expressing the heat tolerant capability of sweet pepper genotypes concerned. Keywords: High temperature stress; performance; sweet pepper. DOI: 10.3329/bjar.v35i3.6459Bangladesh J. Agril. Res. 35(3) : 525-534

Keller et al. (1975). Cultures were exposed to three elevated temperature treatment regimes -35'C for I day; 30"C for 3 days; 35"C for 1 day then 30'C for 6 days (Keller and Armstrong 1979) before being incubated at 25'C in the dark. Embryogenesis was expi'essed in terms of auther productivity (the number of embryos produced by responding anthers) and embryo yield per 1000 anthers (Keller et al. 1982).

The proline contents of anthers, pollen, pistils, and leaves were examined in several tomato (Lycopersicon esculentum Mill.) cultivars under different temperature conditions. The proline content in anthers increased with advancing development of floral buds to a maximum at anthesis. The pistil contained less proline than the anthers and did not accumulate proline with advancement of floral bud development in most cultivars. High temperature reduced proline content in anthers regardless of the stages of floral bud development. It also tended to reduce proline content in pistils of later floral bud stage. The proline content of the leaves was lower than that of anthers or pistils; however, high temperature increased the proline level in the leaves. Pollen collected from the hot-season planting contained less proline than that collected from the cool-season planting. The addition of proline to germination medium enhanced pollen germination rate and increased pollen resistance to heat. These results suggest that the low proline accumulation in anthers and pollen at high temperature may be the result of the high accumulation in the leaves. Also, high proline content in anthers may be necessary to confer heat resistance to pollen germinating at high temperatures.