Comparison of Gamete Selection for Heat Stress and Cool Temperature Tolerance

Abstract

Gamete selection was examined as a breeding tool in developing Phalaenopsis hybrids that are more cool or warm temperature tolerant. Four pairs of hybrid cultivars of Phalaenopsis were cross-pollinated, and then exposed to two temperature extremes, 30 °C / 25 °C and 14 °C/9 °C, during pollen tube development and subsequent fertilization. One of each pollinated orchid cultivar was placed in either of two growth chambers and exposed to an 11-h photoperiod with an irradiance of 180 μmol·m-2·s-1 and a relative humidity of 70% during the day and 50% at night for 3-7 days depending on the temperature treatment. The plants were returned to the greenhouse after the initiation of fruit set and the pods were collected after 150 days. Seeds collected from these treatments were surface-sterilized, placed on Phytamax medium and evaluated for protocorm development after 73 days on a thermogradient table ranging from 10 to 30 °C. 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 scored, 1095 were from cold pollinations, whereas 376 were from the warm pollinations. Additional replication is required to confirm the greater germinability of cold-pollinated seed at higher temperatures.