Lodging due to severe weather conditions is observed in crops each year. A 2‐yr study was conducted to determine the effectiveness of anther‐derived dihaploids for improving lodging resistance, and to examine certain morphological traits which may contribute to lodging in Maryland tobacco (Nicotiana tabacum L.). Forty‐five and 35 dihaploid lines were derived from F1 plants of ‘MD 201’ ✕ ‘Catterton’ (Population 1) and MD 201 ✕ ‘NC 13’ (Population 2) crosses, respectively, using standard anther and midvein culture techniques. Mature plants were subjected to artificially produced wind, and evaluated by a severity rating based on the degree of lean from the vertical position. Significant variation amongth e dihaploid lines was observed for severity rating over the 2 yr. Heritability values for Populations 1 and 2 were 0.61 and 0.64, respectively. Based on severity ratings from the first year field study, five good and five poor dihaploid lines in Population 2 were evaluated in a 2‐yr greenhouse study for top and root fresh weights and top/root ratio (TRR). Significant variation was observed among the 10 dihaploid lines for TRR only; however, the five lines selected for good lodging performance had larger root weights and smaller TRR than the five lines selected for poor lodging performance. Results obtained from these field and greenhouse studies suggest that the development of dihaploid lines with low severity ratings, larger roots, and smaller TRRis possible, and should provide superior genetic material with a good level of lodging resistance.

Lodging of Maryland tobacco (Nicotiana tabacum L.) during the harvesting season may result in lower yields. ‘Maryland 609,’ a cultivar released in 1965, appears more susceptible to lodging than other cultivars. A previous root study with Maryland tobacco has been conducted in the field using the cultivars ‘Catterton’ and ‘Wilson’. These cultivars differed in root growth over a 10‐week period. Studies of this type, however, require considerable time and labor, and the number of plants one can study is often small. Therefore, a greenhouse study was conducted for 2 years with the following objectives: (a) to determine if a simple, but reliable, method could be utilized in the greenhouse for measuring size of tobacco roots, and (b) to determine the amount of variability present among the various Maryland tobacco cultivars for size of roots. Three cultivars (Wilson, Catterton, and Maryland 609) were used in the study during the first year. The number of entries was expanded to six cultivars (Wilson, Catterton, Maryland 609, ‘Maryland 59,’ ‘Maryland 64,’ and ‘Maryland 10’) and three breeding lines (‘M871,’ ‘M872,’ and ‘M881’) during the second year. All entries were grown in clay pots 20.3 cm in diam filled with Galestown loamy sand (Psammentic Hapludult; sandy, siliceous, mesic). Plants were sampled approximately 20, 35, and 50 days after transplanting. Green weight, volume displacement, and dry weight data were obtained on roots and tops. From these results, green weight measurements appeared to be the most simple and reliable for determining size of roots. Wilson had the largest root system of all entries for both years. Maryland 609 had the smallest root system of the three entries during the first year, and was among the group with the smallest roots during the second year. Breeding line M872 had the second largest root system as the plants reached maturity. The amount of variability for root size found among the cultivars and breeding lines suggests that some progress could be made through selecting for increased root size under greenhouse conditions. This increased root size should aid in reducing lodging as the plant reaches maturity.

No abstract

Seven cultivars of Nicotiana tabacum L. (four Maryland and three cigar types) and 21 F1 hybrids were grown at three locations for 2 years. During August, data were collected on leaf damage caused by air pollutants, primarily ozone. This condition was referred to as weather fleck. Ozone causes small necrotic lesions usually 0.2 to 0.5 cm in diameter. Plants were scored on a scale of 1 to 5 (1 = no damage, 5 = severe damage). Comparison of parent (2.34) and F1 hybrid (2.37) performance indicated no significant amounts of heterotic resistance to weather fleck. Diallel analyses of variance of the F1 hybrid generation suggested an appreciable amount of variance due to general combining ability (GCA) and the absence of variance due to specific combining ability (SCA). Genetic effects were stable with respect to locations and years. The genotype × environment interactions for the six environments were small. The predominance of additive genetic variance in this material suggests that progress could be made through selection.

In two alfalfa (Medicago sativa L.) populations, (a) random population of noninbred ‘Vernal’ and (b) a composite S1 population derived from Vernal, the effects of breeding by self‐fertilization and sib‐mating were compared for certain agronomic traits. In general, as the degree of inbreeding increased, there was a reduction in spring vigor, forage yield, seed production, plant height aud width, and an increase in days to flower after first harvest. Also there was a trend toward more upright growth habit. Because the rate of inbreeding was less with sib‐mating than with selfing, the sib‐mated progenies were superior in performance to the selfed progenies.Inbreeding coefficients were computed for the several levels of inbreeding attained, and in general, the reduction observed in forage yield, spring vigor, and seed production was much greater than that expected in an autotetraploid species. The reduction in summer plant height and midsummer flowering was not as great. The use of sib‐mating in a breeding program and reasons for the rapid reduction in performance was discussed.