Genetic analysis of stalk strength in maize

Stalk lodging in maize (Zea mays L.) causes losses estimated to range from 5 to 20% annually in the United States. Selection for rind penetrometer resistance (RPR) has proven useful in enhancing germplasm for stalk strength, and therefore improving stalk lodging resistance. We conducted quantitative trait locus (QTL) analysis for RPR in three F_2:3 populations. Populations were constructed by using combinations of lines selected for high RPR, low RPR, low stalk crushing strength, and inbred line Mo47. Eight, ten, and eight single-effect QTL, and four, two, and zero epistatic interactions were detected for RPR in the three populations, respectively. These data clearly indicate the complex nature of stalk strength. Multi-locus models, including significant single-effect QTL and epistatic interactions, accounted for 33.4%, 44.7%, and 48.4% of the total phenotypic variation. Similar analyses were conducted for plant height (PH), ear height (EH), and resistance to second-generation European corn borer (2-ECB), yielding results similar to those of previous studies.; The correlation between RPR and EH is of interest in understanding response to selection for RPR. Has selection for high RPR resulted primarily in increased stalk strength per se and coincidentally lower ear heights, or has selection for high RPR resulted in lower ear heights and subsequently higher stalk strength? To determine the genetic relationship between RPR and the correlated trait EH, QTL were characterized and compared in each of the three F_2.3 populations for RPR, EH, and RPR adjusted for EH (RadjE). Adjusting RPR for EH caused 11 of the 26 original RPR QTL to lose their significance. However, the majority, 15 of 26, of the original RPR QTL remained significant as QTL for RadjE. These results demonstrated that although EH had a significant effect on RPR as reflected in the negative correlation, QTL analysis can be used to separate genetic effects for RPR per se from genetic effects caused by the correlated trait.; A final objective of this study was to compare the efficiency of phenotypic selection vs. marker-assisted selection (MAS) for RPR and 2-ECB. Marker-assisted selection for high and low RPR was effective in all three populations. Phenotypic selection for both high and low RPR in Populations 1 and 2 was more effective than MAS. However, in Population 3, MAS for high RPR using QTL from Population 3 was more effective than phenotypic selection, and using QTL from Population 4 was just as effective for high RPR as phenotypic selection. These results, therefore, validate the locations and effects of QTL identified for RPR.