Breeding of a high TDN silage maize cultivar, 'Hokko 65', that is adaptable to cold regions of Japan

A new silage maize cultivar, 'Hokko 65', was developed and registered as 'Maize Norin Kou 65' by the Japanese Ministry of Agriculture, Forestry and Fisheries in 2008. 'Hokko 65' is a single cross hybrid between two inbred lines, the dent inbred line 'Ho102' as a seed parent and the flint inbred line 'Ho95' as a pollen parent. 'Hokko 65' is adaptable to the central and southern areas of Hokkaido and the northern Tohoku region. It is classified into the late maturity group in Hokkaido and the early maturity group in Tohoku region. The silking date is one day earlier than that of '35G86' and later than that of '36B08' by one day or less. The whole plant dry matter content of 'Hokko 65' is the same as that of '35G86' and slightly lower than that of '36B08'. 'Hokko 65' shows better early growth than that of '35G86' and '36B08'. Lodging resistance of 'Hokko 65' is higher than that of '35G86' and as high as that of '36B08'. Resistance level of 'Hokko 65' to northern corn leaf blight (Setosphaeria turcica) is high, and the level is slightly higher than that of '35G86' and slightly lower than that of '36B08'. Resistance level of 'Hokko 65' to southern corn leaf blight (Cochliobolus heterostrophus) is moderately strong, and it is as high as that of '35G86' and slightly lower than that of '36B08'. The average dry matter yield of 'Hokko 65' is 5% lower than that of '35G86' and 3% lower than that of '36B08' in Hokkaido, and it is 2% higher than that of '36B08' in northern Tohoku region. The ear content of 'Hokko 65' is higher than those of '35G86' and '36B08' in Hokkaido and is the same as that of '36B08' in northern Tohoku region. The content of the highly digestible fraction (OCC + Oa) and digestibility of fiber (Oa/OCW) in the whole plant of 'Hokko 65' are higher than those of '35G86' and '36B08'. The TDN content in the whole plant of 'Hokko 65' is 2.3 and 1.5 points higher than those of '35G86' and '36B08', respectively. Therefore, TDN yield of 'Hokko 65' is considered to be the same as that of '36B08' in Hokkaido and 5% higher than that of '36B08' in northern Tohoku region. Suitable planting density of 'Hokko 65' is 700 - 780 plants per are, and the adaptability of 'Hokko 65' to higher planting density is as high as that of '35G86' and '36B08'.