A method for evaluating cold tolerance in rice during reproductive growth stages under natural low-temperature conditions in tropical highlands in Kenya

Hiroaki Samejima,Mayumi Kikuta,Keisuke Katura,Daniel Menge,Emily Gichuhi,Cornelius Wainaina,John Kimani,Yoshiaki Inukai,Akira Yamauchi,Daigo Makihara

doi:10.1080/1343943x.2020.1777877

Abstract

ABSTRACT Cold tolerance of New Rice for Africa (NERICA) and their parent varieties was evaluated under natural air temperature conditions of Kenyan tropical highlands using the multiple-sown field evaluation method. Rice varieties were cultivated 10 times to expose them to a shift in temperature during 20-day periods before heading (critical period), measuring the average daily mean temperature during the critical period (Tmean) for each variety and filled grain ratio, which was used as an indicator of cold tolerance. Tmean of each variety was low in 6 out of 10 experiments. In the remaining four high-temperature experiments, there were no significant varietal differences in filled grain ratio. In the six low-temperature experiments, all varieties experienced 20.1−21.5°C Tmean. After comparison under virtually the same cold stress, NERICA 1, 3, 4, 7−10, 12, 17, 18, and WAB 56–104 were judged as cold-tolerant; NERICA 2, 5, 11, 13, and 14, and WAB 56–50 and 181–18 were moderately tolerant, and NERICA 6, 15, and 16 were cold-susceptible varieties. These evaluations generally corresponded with previous experimental results under temperature-controlled environments, showing the practicality of multiple-sown field cold tolerance evaluation in Kenya. It also indicated that NERICA varieties, which recorded different levels of cold tolerance and whose average number of days to heading in all experiments were 66−78, are suitable as a set of standard check varieties in this region to evaluate cold tolerance of rice varieties with this range of days to heading.

Highlights

Cold stress is one of the major constraints to rice production in sub-Saharan Africa
On the condition that New Rice for Africa (NERICA) varieties, i.e. interspecific rice varieties between Oryza sativa and Oryza glaberrima originally devel oped by the Africa Rice Center (Jones, Dingkuhn et al, 1997; Jones, Mande et al, 1997), need rainfall greater than 360 mm in 90 days and air temperature higher than 19°C during the initial reproduction stage, Saito et al (2015) estimated that the area suitable for NERICA cultivation was 2,600,000 ha in Kenya
Based on insights from the seminal work of Satake (1976) and Yoshida (1981), which showed that low temperature most strongly affects rice yield at approximately 10 days before heading, we focused on the period during the 20 days before 50% heading as the critical period, considering differences in heading dates among individual plants within a variety and among tillers within a plant

Summary

Introduction

Cold stress is one of the major constraints to rice production in sub-Saharan Africa. On the condition that New Rice for Africa (NERICA) varieties, i.e. interspecific rice varieties between Oryza sativa and Oryza glaberrima originally devel oped by the Africa Rice Center (Jones, Dingkuhn et al, 1997; Jones, Mande et al, 1997), need rainfall greater than 360 mm in 90 days and air temperature higher than 19°C during the initial reproduction stage, Saito et al (2015) estimated that the area suitable for NERICA cultivation was 2,600,000 ha in Kenya If these varieties can withstand temperature as low as 17°C during the initial reproduction stage, the area would increase by 640,000 ha (Saito et al, 2015). Breeding of coldtolerant varieties has not been actively undertaken in Kenya

Objectives

Methods

Results

Conclusion