Predict Silking Date and Ear Moisture with Corn Heat Units and Other Climatic Factors.
Zhu, X., and Reid, L.M. 2017. Predict Silking Date and Ear Moisture with Corn Heat Units and Other Climatic Factors. 70th Northeast Corn Improvement Conference, Ottawa, ON, Feb 21-22, 2017. Oral presentation.
Silking date and ear moisture are two key factors for corn breeding in short season areas, such as Canada. In a specific short season location, the corn growing season depends on the frost date, so the growth period is limited. If silking is late, the number of days for kernel filling will be less, and this will result in lower yields and higher kernel moistures. Therefore, to predict these two factors and to make silking and filling days balanced, it is important to develop hybrids with higher yields and lower moistures. This study is based on our previous data recorded from our silking date and kernel fast drydown studies. R software packages, MASS, nlme , lme4, agricolar, ggplot2, and their related packages are used for regression analysis. Climatic factors such as daily minimum (Tn) and maximum (Tx) temperatures, daily rainfall, daily bright sunshine hours (Bsh), day length (Dl), and daily total RF1 (Global Solar Radiation, RF1) are used for original data to calculate parameters. Tn and Tx were used to calculate Corn Heat Units (CHU = [1.8*(Tn-4.4)+3.33*(Tx-10)-0.084*(Tx-10)^2]/2) , Growing Degree Days (GDD = (Tn+Tx)/2-10), and General Thermal Index (GTI = FT, FT = 0.043177*[(Tx+Tn)/2]^2-0.000894*[(Tx+Tn)/2]^3). The accumulated data are the total of daily data from sow date to observation date (ACHU= CHU, AGDD= GDD, GTI= FT, Arain== rain, ARFA= RF1, ABSH= Bsh) and accumulated Effective sunshine hours (AESH== (Bsh+(Dl-Bsh)/r), where r is the relative photosynthesis ratio based on mean temperature without bright sunshine, in Ottawa, Ontario, Canada, r=6. Silking days (= silking date – sow date) can be calculated from ACHU, AGDD, GTI, ARF1, ABSH, and AESH divided by their daily means. Among different years, the same genotype has stable AESH, followed by GTI, ACHU, and GDD. AESH*relative photosynthesis rate can be used to calculated silking days when a genotype is introduced to new a location. Silkdays2 = (AESH*relative photosynthesis rate) at location 1/ (mean(ESH)* relative photosynthesis rate) at location2 When prediction with RF1, ACHU, ARF1, and GTI were better than with AGDD; however; only ACHU and Arain, or ARF1 and Arain together can be used to predict silking days. Leaf number, Plant height, ear-leaf length, ear-leaf width, ear-leaf angle, and total leaf area at silking time were highly related to silking days. These plant traits make genotypic difference and can be considered as genotypic effects. Ear and kernel moisture were highly related, but kernel moisture is more difficult to predict than ear moisture, because it is affected by husk and cob moisture. Ear moisture can be predicted by ARF1, ACHU, GTI, and AGDD. Considering the tradition of growers to harvest late corn until spring comes, when the winter is cold, RF1 is more important than temperature indexes. Similar, ACHU and Arain, or ARF1 and Arain can be used to predict ear moisture. Only two kernel traits (density (KGHL) and 100-kernel weight) and one plant trait (Ear-leaf mid-point height) were significantly related with ear moisture; however, kernel density and 100-kernel weight were affected by moisture, therefore, they are not independent variance to be used to predict era moisture. Ear-leaf mid-point height was not good enough to be used to predict ear moisture.
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