Bean common mosaic necrosis virus (BCMNV) includes four African strains, BCMNV-NL3, -NL-5, -NL8, and -TN1, previously considered to be members of the bean common mosaic virus (BCMV) group. Many bean cultivars resistant to BCMNV-NL8 were found to be susceptible to the other strains of the virus. `California Light Red Kidney' (CLRK) and `Carbon', resistant to BCMNV-NL8, were crossed with the susceptible cultivars Sanilac or Black Turtle 2 (BT-2). In plants of F1, F2, and reciprocal backcross populations involving CLRK × `Sanilac' or BT-2 × `Carbon', the resistance to BCMVN-NL8 was determined to be conferred by a single dominant factor. The same factor was detected in BCMNV-NL8-resistant `Great Northern 1140' and `IVT-7214, when crossed with the susceptible cultivar Stringless Refugee or BT-2.
M.M. Welsh and K.F. Grafton
Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Smith) Dye, is a major bacterial disease of dry bean (Phaseolus vulgaris L.). Resistance to common bacterial blight has been identified in other Phaseolus species and resistance genes have been introgressed into P. vulgaris. The objective of this study was to characterize in dry bean the inheritance pattern of common bacterial blight-resistance genes derived from P. coccineus. Two common, bacterial blight-susceptible, dry bean cultivars were crossed with different common, bacterial blight-resistant dry bean lines with resistance derived from P. coccineus. F2 progeny were inoculated with Xanthomonas campestris pv. phaseoli strain F19-W and were scored for disease reaction. The ratio of resistant to susceptible plants for F2 populations did not differ significantly from a 1 resistant: 3 susceptible ratio. The F3 segregation was obtained for only one cross and did not differ significantly from a 1 resistant: 2 heterozygous: 1 susceptible ratio, suggesting that the resistance introgressed from P. coccineus into dry bean was controlled by one recessive gene. Additionally, the range of symptom expression within the susceptible class provided evidence of other genes modifying the expression of resistance.
Thomas M. Davis and James E. Pollard
Robert D. Marquard
More than 30 pecan [Carya illinoensis (Wangenh.) K. Koch] seedlings of `Riverside' have exhibited an unusual leaf morphology described as lace-leafed. Seedlings have relatively low vigor, compound leaves, and leaflets with deeply serrated margins with higher length: width ratios than normal seedings. Some leaves are both pinnate and palmately compound and some leaflets are lobed. The segregation ratio of lace-leafed seedlings for one gene controlling a polymorphic genetic marker supports the hypothesis that lace-leafed seedlings result from selfing of `Riverside.' Nine percent (three of 33) of seedlings derived from selfing of `Riverside' exhibited the lace-leafed morphology, suggesting a recessive trait controlled by one or two genes. The gene(s) controlling this phenotype in pecan is arbitrarily designated the ll gene(s).
Rozlaily Zainol and Dennis P. Stimart
A double-flower form of Nicotiana alata Link & Otto was characterized genetically as a monogenic recessive trait expressed when homozygous. Reciprocal crosses demonstrated no maternal effect on expression of double flowers. A single dominant gene expressed in the homozygous or heterozygous state caused the single-flower phenotype. The symbol fw is proposed to describe the gene controlling double-flower phenotype.
Richard L. Fery and Howard F. Harrison Jr.
Greenhouse and field studies were conducted to determine the genetic relationship between bentazon tolerance exhibited by the pepper (Capsicum annuum L.) cultivars Bohemian Chili and Santaka, and to evaluate the importance of cytoplasmic factors in expression of the tolerance in `Bohemian Chili.' Greenhouse evaluation of parental and F2 populations of the cross `Santaka' × `Bohemian Chili' indicated that the major dominant gene conditioning bentazon tolerance in `Bohemian Chili' is probably the Bzt gene that conditions bentazon tolerance in `Santaka' or a gene closely linked to the Bzt locus. Field evaluation of F1 and F2 progeny populations of the cross `Bohemian Chili' × `Sweet Banana' in both `Bohemian Chili' and `Sweet Banana' cytoplasms demonstrated that cytoplasmic factors do not affect the expression of the bentazon tolerance gene in `Bohemian Chili.' We conclude that `Santaka' and `Bohemian Chili' are equally satisfactory sources of a bentazon tolerance gene for use in pepper breeding programs. Chemical name used: 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon).
Tommy E. Thompson and L.J. Grauke
R. Messina, R. Testolin, and M. Morgante
The usefulness of isozyme banding patterns as genetic markers in kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson] was investigated using starch gel electrophoresis. Fifty-four entries putatively belonging to seven female and two male kiwifruit cultivars were examined for 13 enzyme systems (AAT, ACO, GDH, G6PDH, IDH, MDH, ME, MNR, NDH, 6PGD, PGI, PGM, and SKDH). Four enzyme systems, ACO, MDH, NDH, and SKDH, showed identical banding patterns in all clones surveyed. Of the remaining enzymes, AAT, PGI, and PGM had the best discriminating power. Six enzyme systems (GDH, G6PDH, IDH, ME, MNR, and 6PGD), though showing polymorphic banding patterns, were poorly resolved. All the New Zealand cultivars were uniquely identified by the simultaneous comparison of the AAT, PGI, and PGM zymograms. Some enzyme systems were also polymorphic among plants within the same cultivar, thus proving the heterogeneity of kiwifruit material introduced into Europe in the early 1970s.
T.E. Thompson and L.J. Grauke
The U.S. Dept. of Agriculture, Agricultural Research Service conducts the largest and oldest pecan [Carya illinoinensis (Wangenh.) K. Koch] breeding program in the world. This program evaluates thousands of nut and kernel samples each year using a standard nut and kernel evaluation system developed and refined for more than 70 years. This report relates the effectiveness of these evaluations to commercial shelling efficiency by direct comparison of these data to commercially shelled samples from the same clone performance test. Visual ratings of shelled kernel samples (1-5, with 1 = best) were correlated with time required to hand clean kernel samples (r = 0.55). As percent kernel increased, visual ratings of shelled kernels improved (decreased) (r = -0.73). More intact halves were recovered from shelled samples with the best (lowest) visual ratings (r = -0.67). Conversely, fewer pieces of any size were present in samples with the best visual ratings. Visual ratings improved as nut density decreased (r = 0.33). Samples with the lightest kernel color also had the best visual ratings (r = 0.38). These data show that the standard U.S. Dept. of Agriculture pecan nut and kernel evaluation system needs to be refined by modifying selection pressure placed on various standard evaluation traits.