Assessment of temperature responses of in vitro pollen germination, cell membrane thermostability, and chlorophyll stability among six guava (Psidium guajava L.) varieties cultivated in Sri Lanka

Abstract

Understanding trait variation in response to temperature is important to predict how plants respond to rising temperature. This study aimed to identify heat-tolerant Guava (Psidium guajava) varieties through assessment of physiological and reproductive performance assessment. The experiment was conducted at the Fruit Research and Development Institute, Horana, Sri Lanka. Six widely growing Guava varieties viz. Horana White, Horana Red, Horana Rosi, Apple guava, Kanthi and Lanka Giant that grown at a common temperature (28°C) were evaluated for reproductive and physiological heat tolerance. In vitro pollen germination percentage (PG) and pollen tube growth (PTL) were quantified by incubating pollen samples in a liquid germination solution across temperatures ranging from 18 and 40°C. Physiological traits, including cell membrane thermostability (CMT) and chlorophyll stability index (CSI) of fully expanded leaves, were measured following standard protocols. Data for each variety were collected from three randomly selected mature plants (3-replicates) arranged in a completely randomized design. Cardinal temperatures (minimum, optimum and maximum) for pollen germination and pollen tube growth, along with maximum pollen germination percentage and maximum pollen tube length, were estimated by fitting nonlinear regression models using R software. Both pollen germination percentage and pollen tube length increased with temperature up to 28°C, then declined at higher temperatures. Optimum temperatures for pollen germination and pollen tube growth did not differsignificantly among varieties (28°C for both). In contrast, the physiological traits CMT and CSI differed significantly between varieties. The variety “Pubudu” exhibited significantly higher chlorophyll stability index than other varieties, while “Horana white”, “Kanthi”, and “Pubudu” showed significantly higher CMT values compared to the other three varieties. These results suggest that “Pubudu” possesses superior cell membrane thermostability and chlorophyll stability under elevated temperatures and can be considered a potential heat-tolerant variety.