Germination of guar (Cyamopsis tetragonoloba (L.) Taub.) genotypes with reduced temperature requirements

Guar (Cyamopsis tetragonoloba (L.) Taub.) is an annual legume species with a medium late crop cycle (> 160 days) and relatively high temperature requirements for seed germination (20-21°C). In Mediterranean areas, such temperatures result in sowing times no earlier than late May-early June and, consequently, late harvests in November, usually after a very rainy period in late summer/early autumn, which can result in severe damage to yield quality. Furthermore, such late harvests usually conflict with the seeding requirements of winter crops (such as wheat), which are very frequent in Mediterranean crop rotation systems. Therefore, the availability of genotypes with low temperature requirements seems to be a key factor for the introduction of guar in Mediterranean areas, which motivated our research. The germination of nine guar genotypes coming from different geographic regions was tested at seven constant temperatures (5, 10, 15, 20, 25, 30, 35°C) plus two alternating temperatures (15/10°C 6/18 hours and 20/15°C 6/18 hours thermal period). The results proved that, while optimal temperatures were always from 30 to 35°C, some genotypes are characterised by satisfactory germination capability also at constant temperatures as low as 15°C, e.g. the Indian genotypes (33-43%) and, to a lesser extent, Pakistan and Monument (27-28%). Furthermore, germination capability was significantly improved in the case of alternating temperatures (20/15°C) as long as the highest temperature was maintained for 6 h per day (Kinman reached up 80%, India2 76% and Monument 66%). As this alternating temperature condition is rather common in the soil during Mediterranean springs, our results might be useful for farmers to optimise the seeding time/rate for guar. Our results could also support breeding studies, aimed at crossing genotypes that tolerate low germination temperatures with genotypes that possess high yield potential levels.