Excess soil water following planting adversely affects the establishment and early growth of barley seedlings. So, flooding-tolerant cultivars are desirable in southern Japan where the barley is usually grown soon after the paddy rice cropping. Thus, the varietal variation for flooding tolerance in ca. 3,400 barley varieties of the world collection was examined under laboratory condition.

A preliminary examination revealed that in some sensitive varieties the germinability was injured by two-day soaking, while in some tolerant varieties seed viability was remained after six- day soaking in water at 25 C temperature condition. For testing the flooding tolerance of enormous number of varieties the following method was devised: Fifty seeds each were sterilized with a fungicide and were submerged in deionized water in a test tube for four days at 25 C, and then the germinability of the seeds was examined after four days on a moistened filter paper set in a Petri dish at 25 C. As seed quality significantly affected the flooding sensitivity, those varieties with more than 96% germinability under the ordinary condition were employed for the test of tolerance. Germination percentage of the soaked seeds was adopted for the index of flooding tolerance.

Varietal variation for the index was as large as 0 to 100, i.e., complete death to no-damage of the soaked seeds (Table 1). Collections from China, Japan and Korea contained many tolerant varieties, while those from North Africa and Southwest Asia contained very few tolerant ones. This may suggest the effect of natural selection for the flooding tolerance through climatic condition of the regions.

A further investigation revealed that the most tolerant varieties retained complete germinability after eight-day soaking at 25 C temperature. These varieties may be a good genetic resource for improving the flooding tolerance of barley varieties. Mechanism and genetics of the trait is the future subject.