Cultivar-dependent fruit malformation in strawberry (Fragaria X ananassa Duch.) due to high temperature stress

Fruit malformation is a common problem in commercial strawberry production around the world. Malformed strawberry fruits cause significant yield losses because they are considered unmarketable. In strawberry, fruit malformation is inherently linked to achene functionality. Several factors are known to damage achenes. These include disease and insect attack, low temperature and frost, and high nitrogen fertilizers. Studies on the effect of high temperatures on strawberry reproduction have recently received focus because of concerns about the effect of climate change on this temperate crop and an interest in commercial production in tropical countries such as the Philippines. In this paper, we show that high temperature conditions can also cause fruit malformation in strawberry, but the response varies by cultivar. Strawberry cultivars \u27Nyoho\u27 and \u27Toyonoka\u27 were grown at 23/l 8°C (NT) or 30/25°C (HT) at the start of their reproductive stage until fruit maturity. All ripened fruits were harvested, photographed then rated as either well-shaped (normal) or malformed (slight to severe, MF). The number and condition of the achenes were determined from the photographs and rated as either fertile (red/green and swollen) or undeveloped/aborted (green and shrunken, UA). Results showed a significant difference in the incidence of fruit malformation between temperature treatments and between cultivars. At NT, both cultivars had a low incidence of MF (14-16%). At HT, the percentage of MF significantly increased in both cul ti vars, but Toyonoka produced more MF (80%) than Nyoho (44%). The same response was observed in the achenes. There were more UA achenes at HT than at NT. Toyonoka also produced more UA achenes than Nyoho at HT. Data from the first and second inflorescences of both cultivars also significantly differed. These results show that exposure to high temperatures can significantly affect the quality and marketability of strawberry fruits, but the response is cul ti var dependent. Nyoho is more tolerant to high temperatures and may be a better candidate for commercial production in tropical conditions or as germplasm for breeding for heat tolerance in strawberry