Genotype and environment influence on the rate of grain moisture loss in corn during ripening period

High grain moisture during harvesting is a factor that restrains the expansion of corn ( Zea mays L.) crops in the Ural region. A decrease in the harvesting moisture content of seeds is achieved by corn breeding for early maturity (early flowering of the ear) and for accelerated moisture loss from grain in the pre-harvesting period. In our study, it was found for the first time that in the conditions of southern Russia under weather conditions that weakly limit moisture losses, the harvesting moisture of corn grain is determined by the rate of pre-harvesting moisture losses while in the Ural region where the weather conditions are periodically unfavorable the moisture losses are mainly due to the early maturity of the studied hybrids. This work aims to identify corn hybrids with an increased rate of moisture loss during grain ripening and to assess this trait under unfavorable hydrothermal conditions. The studies were carried out in 2016-2018 in two contrasting geographical sites, in the foothill zone of the North Caucasus (experimental field of the All-Russian Research Institute of Corn, the settlement Pyatigorskiy, Predgornii District of the Stavropol Territory) and in the northern forest-steppe of the Southern Urals (South Ural GAU, village Miasskoye, Krasnoarmeyskiy District, the Chelyabinsk Province). Six ultra-early corn hybrids ( Zea mays L.) Nur, Ross 130 MV, Obsky 140 SV, Kubansky 141 SV, Mashuk 150 MV, Uralskiy 150 and early ripening Bilyar 160 hybrid were involved in the study. The field experiment was arranged in triplicate using a randomized field plot layout (28 m2 plots with a full set of hybrids per plot). The recorded phenological phases were germination, ear flowering and physiological ripeness of grain detected by the corn kernel “black layer” as an indicator of physiological maturity. The corn grain moisture was measured gravimetrically from July 25 to September 11 in the North Caucasus and from August 15 to October 10 in the South Urals. Samples weighting not less than 70 g were dried at 150 °С to a constant weight (a SNOL 58/350 exicator, Elektrotechnika, AB, Republic of Lithuania; a CAS MW-II electronic Weighing Scale, CAS Corporation, Republic of Korea). For analysis, 10 ears of 1.2 to 1.8 kg were collected and completely threshed in three reps. Grain sampling was carried out with a 3-7-day intervals providing 8 to 16 control points. Statistical hypotheses were tested by methods of variance, correlation and regression analysis. It was found that in the northern site, the calendar dates of flowering of the ear occurred in the beginning or end of the third decade of July, that is, 22-36 days later than in the south site. In the conditions of the North Caucasus, flowering occurred in the third decade of June-early July, the grain physiological ripeness was reached from 1 to 7 August, that is, grain maturation and filling in ultra-early maturing hybrids occurred under favorable hydrothermal conditions. Consequently, environmental conditions did not limit the rate of moisture loss in grain, which provided reliable estimates of the differences between hybrids according to the trait. The research revealed significant differences in the rate of moisture loss both between the study sites and the hybrids. In the North Caucasian region, the rate of moisture loss in grain after reaching physiological ripeness varied for hybrids from 0.63 to 0.78 % per day with slight variation over the years. Under higher relative humidity and low air temperature the likelihood of which in the pre-harvest period is high for the Ural region, the rate of moisture loss decreased to 0.21-0.35 % per day, and under favorable hydrothermal conditions it reached only 0.52-0.72 % per day. It has been established that the harvest moisture content of corn grain is associated with two main characteristics of hybrids, i.e., the early maturity and the ability to quickly lose moisture at the final stages of ontogenesis. The contribution of each factor is due to the conditions of grain ripening. I.e., for the south of Russia, grain moisture is largely due to the ability of a hybrid to accelerate moisture losses. On the contrary, in the conditions of the Southern Urals, the early flowering of the ear is of primary importance. Differences between hybrids in the rate of moisture loss under these conditions appear irregularly and are often leveled by the influence of the environment. Therefore, for the northern zone of corn sowing, the corn breeding for its ability to rapidly lose moisture from grain makes sense only in combination with breeding for a short growing season which should be considered as a priority trait when creating adapted hybrids.