Low temperature germinability and ABA sensitivity in wheat cultivars with pre-harvest sprouting tolerance

Y. Ichinose^1*, T. Kuwabara², N. Iriki³ and K. Takata<sup>2

1</sup> National Institute of Crop Science, Tsukuba, Ibaraki 305-8518, Japan
² Dept. of Upland Agriculture Research, National Agricultural Research Center for Hokkaido Region, Memuro, 082-0071, Japan
³National Agricultural Research Center for Hokkaido Region, Sapporo, 062-8555, Japan

Summary

To prevent pre-harvest sprouting (PHS) in wheat, selection of genotypes that maintain dormancy and imbibe even at low temperature during grain development is receiving considerable attention in breeding programs. However, little information is available for the genetic variation in low temperature germinability and its relation to the abscisic acid (ABA) sensitivity of an embryo. To evaluate low temperature germinability and ABA sensitivity, grains of 30 cultivars with various levels of PHS tolerance were incubated in water or an ABA solution at different temperatures. When grains at the dough-ripe stage were germinated at 12°C, grain germinability and ABA sensitivity varied even in PHS-tolerant cultivars. The dormancy of some PHS-tolerant cultivars broke with loss of ABA sensitivity at low temperature, suggesting that tolerance to PHS is in part genetically independent of low temperature germinability. A close relationship was found between, low temperature germinability and the ABA sensitivity. For wheat production under cool moist conditions at maturity, it would be significant to develop cultivars that did not germinate at low temperature.

Key words: abscisic acid, low temperature germinability, pre-harvest sprouting, grain dormancy, Triticum aestivum

Introduction

Wheat (Triticum aestivum L.) cultivars are characterized by relatively weak embryo dormancy, and, under cool moist conditions at maturity, they show a developmental disorder and pre-harvest sprouting (PHS). PHS reduces grain yield and leads to deterioration in the milling performance and quality of the end product. The PHS problem often occurs in many major wheat growing areas of the world (Allan 2000). As reviewed by Li and Foley (1997), several morphological and physiological traits influence the expression of PHS, and grain dormancy is considered to be the most important factor in controlling PHS damage.

While high levels of dormancy are required to improve wheat cultivars, many environmental factors influence dormancy. Temperature and moisture during grain development and after ripening are especially important (George 1967; King 1993). While it has been reported that low temperatures during grain development enhance the level of grain dormancy (Kuwabara and Maeda 1979), mature wheat grains show dormancy when incubated at above 20°C but not below 12°C (Bewley and Black 1994). In turn, dormancy breaking at low temperature would lead to a problem in several wheat production areas where grain develops under relatively high humidity and cool temperatures of 12°C or less. This is the case in Japan, especially in Hokkaido. Therefore, selection of genotypes that maintain dormancy and imbibe even at low temperature during grain development has received considerable attention in breeding programs (Osanai and Amano 1996; Amano et al. 1999; Osanai and Amano 1999). By recurrent selection for low temperature germinability, Osanai and Amano (1993) developed a series of genotypes that are tolerant to PHS because they lack altogether or have weak low temperature germinability. On the other hand, Walker-Simmons (1987) indicated that the abscisic acid (ABA) sensitivity of the embryo was related to grain dormancy and PHS resistance. Noda and Kanzaki (1988) reported on the effectiveness of selection for ABA-sensitive genotypes by applying ABA to whole grains that almost lacked grain dormancy. This was done because embryo sensitivity to ABA of a PHS-tolerant cultivar is maintained even after its dormancy disappears. However, little information is available for genetic variation in low temperature germinability and its relation to the ABA sensitivity of the embryo.

In the present study, to evaluate the low temperature germinability and ABA sensitivity, germination tests were conducted at different incubation temperatures using 30 cultivars with various levels of PHS tolerance.