Bacterial blight, incited by Xanthomonas axonopodis pv. vignicola, is a major disease of cowpea. Strong resistance has not been reported in commercial cultivars. Many cultivars released within the last ten years have not been previously screened. Thirty-eight cowpea cultivars, 60 breeding lines, and 25 PIs were screened for reaction to bacterial blight in tests conducted in a greenhouse. Inoculum was adjusted turbidimetrically (OD620nm = 0.1) to approximately 108 cfu/ml. Seedling plants were inoculated by either leaf infiltration or stem puncture methods. Ratings were on a 1-6 scale in which 1 = no symptoms, 2 = localized lesions at site of inoculation, 3 = lesions spreading slightly near site of inoculation, 4 = any symptoms on systemically infected leaves or stems, 5 = extensive wilting and/or stem collapse, 6 = dead plant. All cultivars were susceptible to the pathogen. Cream-type cultivars Bettergreen, Tender Cream, Zipper Cream, Carolina Cream, and Mississippi Cream were among the most susceptible. Breeding lines MN13, MN150, TX57069-11, TX 58048-2000, and TX 59069-11 produced hypersensitive reactions in response to leaf infiltration inoculation. However, the three TX lines were rated susceptible when inoculated by stem puncture. Eighteen PIs (including PI293467, PI293521, PI293525, PI293567, and PI293571) were highly resistant to bacterial blight.
Blair Buckley III and Christopher A. Clark
Blair Buckley III and Katharine C. Pee
A force gauge was used to measure the force required to detach pods from plants of 16 southernpea [Vigna unguiculata (L.) Walp.] cultigens. Pod detachment force (PDF) measurements ranged from 21.4 N for MN-13 to 11.8 N for `Royal Cream'. Pod length, diameter, and weight; basal pod vacancy (inverse of fill); and peduncle synapse length were recorded for each pod sampled for detachment force. There was no strong association between PDF and any of the five traits.
Blair Buckley III and Katharine C. Pee
An investigation was conducted in 1993 and 1994 to examine the effect of row spacing on yield and pod maturity distribution of machine-harvested, green-mature southernpeas [Vigna unguiculata (L.) Walp]. `Texas Pinkeye Purple Hull' was planted at row spacings of 53, 89, and 107 cm single drilled and 107 cm double drilled. Marketable yield increased linearly as row spacing decreased. A double drill on a standard 107-cm row spacing did not result in higher yield than a single drill. Marketable yield from the double-drilled, 107-cm row spacing was less than yield from the 53-cm spacing. The seeding rate per hectare for the two treatments was the same. In 1993, the mature pod percentage at harvest increased linearly as row spacing decreased. Row spacings as narrow as 53 cm can be used to increase yield of machine-harvested, green-mature southernpeas.
Blair Buckley III, James N. Moore and John R. Clark
Rosette, incited by Cercosporella rubi (G. Wint.) Plakidas, is the most severe disease of blackberries in the southern United States. Sixteen blackberry cultivars and breeding selections were evaluated in a field test over a 3-year period for incidence and severity of rosette. Test plots were planted in a randomized complete block design with four replications. A plot consisted of a 3-m hedgerow of blackberry canes. Each test plot row was bordered on each side by a row of the rosette-susceptible cultivar Shawnee. Disease ratings were conducted on five random floricanes in each plot. Disease severity was rated with a 1 to 8 scale (1 = 0% floricane nodes with rosettes, 2 = 0% to 10%, 3 = 10% to 25%, 4 = 25% to 50%, 5 =50% to 75%, 6 = 75% to 90%, 7 = 90% to 100%, 8 = 100%). `Shawnee' and `Rosborough' had high incidence and severity. Cultivars and selections with moderate-high incidence and low-moderate severity were `Brazos', `Cheyenne', `Choctaw', A-1260, A-1442, A-1560, and A-1585. Cultivars and selections with zero-low incidence and severity were `Arapaho', `Humble', `Navaho', A-1374, A-1594, A-1616, and A-1617.