Background: Stem lodging seriously restricts the development of mechanized maize harvesting. However, currently there is no comprehensive stem strength evaluation standard for cultivating new maize varieties with excellent stem performance that are suitable for mechanical harvesting. In this study, we constructed a panel of maize germplasm accessions with various stem strengths by setting up different levels of stalk-rot resistance. We investigated the factors influencing maize stem strength, as well as the relationships among them to clarify the key indices for evaluating stem strength.
Results: Our results indicated that the stem density, moisture content, bending strength and rind puncture strength were responsive to stalk-rot resistance. However, these indices were in agreement with stem resistance only after the physiological maturity of maize. In particular, the stem rind puncture strength exhibited a closer correlation with the stem resistance in the late stage of physiological maturity. It was also demonstrated that stem density directly affected bending strength and rind puncture strength, whereas indirectly affected the elastic modulus. The elastic modulus includes both load and displacement; therefore, it can prompt the reliability of stem strength evaluation, and is the best description of stalk toughness. The attenuation amplitude of the elastic modulus is always the largest whether it is caused by the aggravation of the disease, the growth stage delay, or the internode position rise, which significantly improves the sensitivity of stalk strength evaluation. Our results showed that the elastic modulus was correspondent with stem resistance from the silking stage of maize, which not only effectively improved the accuracy of the stalk strength evaluation, but also was extremely beneficial to improve the efficiency of maize variety selection.
Conclusions: The elastic modulus can be used to evaluate the maize stem strength truly and accurately, and especially in the high stalk rot incidence region, it is very beneficial to improve the breeding efficiency of the maize varieties suitable for mechanical harvesting.