In 2003, severe barrenness due to low temperatures in hybrid maize (Zea mays L.) cultivar occurred in the Konsen region, one of the coldest areas in Japan. Varietal difference in grain set, and abnormal flowering habits and tassel growth were observed in the field in 2003. For the cultivar 39B29, which was affected severely, anthesis occurred several days after silking, and tassel size was reduced. For the cultivar Papirika, which was not affected by low temperature, anthesis began 0-1 d before silking, and tassel size was similar to that in previous years. In a 2011-2013 experiment, three varieties, Papirika, 39B29, and Kwiss were treated at 10 °C for 7 d at 6-to 9-leaf stage. Following the treatment, anthesis was delayed, and tassel length was reduced, in 39B29 and Kwiss, but not in Papirika. The relative tassel length (RTL, ratio of tassel length of experimental plants to that of untreated control plants) was around 60 in 39B29, 80 in Papirika, and 30 in Kwiss on average over 3 years. Based on field observations in 2003 and the pot experiment in 2011-2013, a cultivar whose RTL was 60 or less was deemed sensitive, and a cultivar whose RTL was 80 or more was deemed less sensitive to lowtemperature stress during the tassel development stage.
Mixed seeded plots of timothy (Phleum pratense L.) and galega (Galega orientalis Lam.) were established in multiple seeding times from 2014 to 2017 to determine the latest sowing limit in the Konsen region, northern Japan, where growing conditions are severe. Although low yields were observed in some cases when the soil freezing depth was deeper than average, the dry matter yield of the first crop of galega in the year after sowing was higher under conditions that ensured pre-overwintering plant length growth of 30 cm or more, as compared with growth of less than 30 cm. Galega rhizomes were observed under conditions of pre-overwintering plant length of 28 cm or more, but not under conditions of less than 28 cm in length. Therefore, achieving 30 cm plant length prior to overwintering is desirable when sowing galega in the Konsen region. Furthermore, the effective cumulative temperature (ECT) required for pre-overwintering galega to reach 30 cm in plant length was 1079 C, for which seeding dates were calculated to be July 10 and June 29 in terms of calendar days, with 80% and 90% probability. In the Konsen region, galega should be sown earlier than in other regions of Hokkaido to ensure the growth rate because of the effects of soil freezing on overwintering performance.
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