Effects of high temperature on pollen quality, ovule fertilization and development of embryo and achene in 'tochiotome' strawberry

Abstract

Effects of high temperature (HT) on pollen quality, ovule fertilization and development of embryo and achene were investigated in relation to fruit malformation in 'Tochiotome' strawberry (Fragaria X ananassa Duch.). When the flower bud of the first inflorescence was developing, plants were transferred to HT (32/27°C) and control temperature (CT: 27/22°C) rooms. At anthesis, anthers were collected from flowers in the first (1st) and second (2nd) inflorescences to examine pollen viability and germination. Both viability and germination were not significantly different between the two temperatures and inflorescences. Approximately 90-93% of ovules were fertilized under CT in both inflorescences; however, the fertilized percentage of ovules in HT-lst was only 52% and significantly increased to 85% in HT-2nd. Embryo development in both inflorescences was accelerated by HT: embryos from HT regimes were in heart- and torpedo-shaped stages at 6 and 8 DAP while those of CT were still in globular- and heart-shaped stage. The transverse and longitudinal lengths of embryos under HT increased more rapidly than under CT. Embryo abortion in the globular stage was found at 2 and 6 DAP under HT-2nd. Relationships between the percentages of three types of achenes (unfertilized (Un), aborted (Ab), and normally developed (Nd) achenes) and degrees of fruit malformation were examined. Ripe fruits were graded into five fruit shape scores (0-4), 0=well shaped fruit, and 4=severely malformed. Nd achenes in CT-lst and CT-2nd were approximately 70% with fruit shape score; 0.8 and 0.2, respectively, whereas those in HT-lst and HT-2nd were 38 and 54% with high malformed shape score: 2.8 and 1.8. Un achene in HT-lst was 45%, while only 9% was found in HT-2nd. The Ab achenes rate was remarkably increased to 31% in HT-2nd treatment, these suggesting that the sudden rise of temperature after flower bud initiation lowered the ovule fertilization rate and raised the unfertilized achene rate, resulting in a high degree of fruit malformation in HT-lst, while longer HT increased achene abortion during early embryogenesis due to low pistil potential, and finally induced fruit malformation in HT-2nd. JSHS © 2009.