GAMETOPHYTIC SELECTION FOR THERMOTOLERANCE IN PHALAENOPSIS By

Gametophytic selection was examined as a breeding tool in developing Phalaenopsis hybrids that are more cool or warm temperature tolerant. Two hybrid Phalaenopsis, P. (Taisoco Windian × Sogo Yukidian) by P. hybrid unknown, were reciprocally crosspollinated and exposed to 14°C/9°C for 7 days as a cold pollination treatment. Plants were pollinated again and exposed to 30°C/25°C for 3 days for the warm pollination treatment. Each cultivar was placed in either of two growth chambers during the pollination treatments and exposed to the selected temperatures, an 11-h photoperiod with an irradiance of 180 Mmol•m•s and a relative humidity of 70%. The plants were returned to the greenhouse after pollination and the green capsules were collected after 150 days. Seeds obtained from these treatments were surface-sterilized and equal volumes were placed on Phytamax® medium. Evaluation of protocorm development was done after 73 days on a thermogradient table ranging from 10 to 30oC. For the first family for which reciprocal crosses were available, the number of protocorms per plate ranged from 0 in the coldest treatments to 290 at 28°C. For cold pollinated seeds, protocorm development was optimum at 22 and 28°C (means of 290 and 250 protocorms per plate, respectively) whereas the greatest protocorm development for warm pollinated seeds occurred at 20°C (103 protocorms per plate). Of the 1471 total protocorms obtained 1095 were from cold pollinations, whereas 376 were from the warm pollinations. Protocorms were evaluated for leaf and root formation 125 days after initial plating. Transfer to warm or cold incubators occurred as protocorms developed leaves and roots. Seedlings were finally transferred to dried sphagnum and placed in growth chambers set to original pollination temperatures. One year after initial plating seedlings were evaluated on the following criteria: wet weight, number of leaves, leaf area, number of roots, and root length. The pollination treatment significantly affected the number of roots per seedling whereas germination temperature during germination significantly affected the weight (g). Weight of the seedlings, number of roots and the average root