In an attempt to find better ways of estimating relative maturity differences in corn (Zea mays L.), various thermal unit formulas were evaluated. Utilizing data from six plantings of corn over a 2 year period, 22 different methods of computing thermal units were tested for their ability to account for variation in flowering dates. Both hourly and daily temperature data were used in the equations. In general the daily measurements appeared to be approximately as accurate as the hourly measurements. The best equation for predicting flowering dates on the basis of thermal units utilized a base temperature of 10C (50F) and an optimum of 30C (86F). The excess temperature above 30C was subtracted to account for high temperature stress.

A diallel cross of seven inbred lines of corn (Zea mays L.) was examined for duration of the grain‐filling period, rate of fill, and associated agronomi characters to determine the practicability of selection for these traits. The length of the grain‐filling period and the rate of grain filling differed among hybrids and between years, but interactions between years and hybrids were not detected. Hybrids did not differ for duration of the lag phase of the grain‐filling period.The general combining ability effects for duration and rate of grain filling were larger than specific combining ability effects which snggested that simple selection techniques should be effective in changing these characters within the material studied. A phenotypic correlation of 0.81 was found between duration of the grain‐filling period and grain yield, while the correlation between rate of fill and grain yield was nonsignificant.Although the association between duration of the filling period and ear moisture content at harvest was high (r = 0.82), there was some evidence that it might be possible to shorten the vegetative period without sacrificing yield.

Fusarium wilt in common bean (Phaseolus vulgaris L.) caused by Fusarium oxysporum Schlechtend. Fr. forma specialis phaseoli Kendrick and Snyder (Fop) occurs worldwide and can result in severe yield loss. Because cultural methods to control disease loss are not completely effective, cultivars with genetic resistance are needed. The objectives of this study were to determine whether genetic control of resistance to Fop race 4 differs between germplasm of races Durango and Mesoamerica of common bean and to estimate heritability of resistance found in race Mesoamerica. Resistant and susceptible lines of races Durango and Mesoamerica were crossed within races to produce F2 and F3 progeny. Reaction to Fop was evaluated using a root‐dip inoculation method and scored using a CIAT disease severity scale from one to nine. F2 populations derived from race Durango parents showed a 3:1 (resistant/susceptible) plant segregation ratio, and F3 progeny tests confirmed that resistance was controlled by a single dominant gene. F2 data from crosses between parents of race Mesoamerica had continuous distributions for reaction to Fop race 4, suggesting polygenic control of resistance. The narrow‐sense heritability estimate derived from midparent–offspring regression of 10 F2 populations derived from Mesoamerican parents was 0.85 ± 0.34, and realized heritability estimates ranged from 0.25 ± 0.19 to 0.60 ± 0.16 among five populations. The heritability estimates as well as the continuous variation in disease severity observed support the hypothesis that resistance to Fop race 4 among parents of race Mesoamerican is polygenic.

Rewiwl 10 April I984 INDEX WORDS Zeamays, maize, ear moisture, dry-down rate. SUMMARY A selection procedure to change the drying rates of maize (Z~LI mays L.) ears was developed and tested. Results indicated that drying rates were affected by hybrid genotype, ear maturity at harvest, number of kernels per row, ear diameter.and moisture content at harvest. Mass selection was initiated in an early synthetic, NDSG, in an attempt to produce both fast and slow drying strains. After two cycles resultant substrains were evaluated in the laboratory for direct and in the field for correlated selection responses. Laboratory results indicated that selection effectively changed moisture loss rates in NDSG, and confirmed earlier observations that an ear's moisture content at harvest affects its drying rate.Data from field experiments grown at five locations in 1980 revealed that each of two selection cycles for slow laboratory drying rate significantly reduced ear moisture content at harvest, in the field. This lower harvest moisture content appeared to result from a lower moisture content at physiological maturity rather than a faster drying rate. Other correlated selection responses included lowered yield. plant height. and ear weight due to selection for fast laboratory drying, and lowered plant height and ear weight from selection for slow drying.Data indicated that this selection procedure can be used to change moisture loss rate and ear moisture content at harvest. Results also contributed to understanding of factors involved in ear drying rates which may lead to more effective selection procedures.

Two procedures to change ear drying rates were tested in five early maize (Zea mays L.) synthetics for their relative merits for breeding varieties adaptable to more timely harvest, which requires less grain drying and possession of acceptable agronomic characteristics. Objectives of this study were to assess the relative effectiveness of a laboratory and a field selection method for improving harvest moisture contents and to measure any correlated responses for other agronomic traits. Substrains in each synthetic, divergently selected for two or more cycles for relative rates of moisture loss from ears in the laboratory were evaluated in six environments along with substrains divergently selected for two cycles for ear moisture content at 45 days postpollination. Regression procedures were used to evaluate selection responses for ear moisture at harvest and correlated responses of other agronomic traits. Selection for slow relative moisture loss in the laboratory (SD) changed field harvest moisture by-6.73 g kg ' cycle ~' and produced correlated reductions in ear length, kernels per ear, kernel rows per ear, ear weight, and root lodging. Selection for low ear moisture at 45 days postpollination (LM) changed harvest ear moisture in selected strains by-7.15 g kg" 1 cycle" 1. Correlated increases in test weight and decreases in stalk lodging also were observed. Selection for fast relative moisture loss in the laboratory (FD) or high moisture content at 45 days postpollination (HM) generally produced increased ear moisture at harvest in selected strains. Neither yield nor silking dates were changed by the selection methods. Harvest moisture responses from the SD method seemingly resulted from reduced moisture content at 45 days postpollination rather than changes in the rate of moisture loss from the ear. Whether selection has produced basic changes in endosperm composition remains to be determined. The LM method appears very feasible for practical breeding programs because of simplicity and effectiveness.