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The Agricultural Research Service of the United States Department of Agriculture announced the release of `Bettergro Blackeye' southernpea on 24 July 1991. The new cultivar is well adapted for production throughout the southern United States where it can be expected to produce excellent yields of high quality, blackeye-type peas. `Bettergro Blackeye' outyielded the `Pinkeye Purple Hull-BVR' check in the 1986, 1987, 1988, and 1989 Regional Southernpea Cooperative Trials by 34.8, 14.3, 12.6, and 20.9%, respectively. Canned samples of fresh `Bettergro Blackeye' peas scored well in three years of quality evaluation tests. The new cultivar is resistant to the cowpea curculio, the major insect pest of the southernpea in southeastern production areas, and root knot, a severe root disease incited by several species of the root-knot nematode. `Bettergro Blackeye' plants have a greater tendency to produce a second crop than plants of most southernpea cultivars.
There are four known physiological races of the southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood]. Races are designated I through 4 and their identifications are based soley on differential hosts. These race problems as related to breeding sweetpotato for resistance to attack by all races are reviewed and discussed. Data are presented showing the reactions of selected cultivar and breeding clones of sweetpotato to all four races. The reactions of races 1 and 3 are generally well—known. Races 2 and 4 apparently are spreading and becoming more numerous in the southern states where soybean and tobacco are grown. Comparative disease indices are presented showing that generally sweetpotatoes were less susceptible to races 2 and 4. However, there were some notable exceptions, for example, `Sulfur' and `Beauregard' were equally susceptible to all races. High resistances to attack by races 2 and 4 were found in `Sumor', `Nemagold', `Excel', W-241 and others.
Abstract
Thirty random seedlings from each of 50 random parents of a sweet potato (Ipomoea batatas (L.) Lam.) mass selected population were evaluated in the greenhouse and their subsequent field performances were recorded. Simulated selection sequences were also studied. A sequence with mass selection first on maternal hill weight, high seed set, and high seed weight followed by a 50% culling level within families on the basis of low greenhouse seedling vigor resulted in average progeny field yields 45% above that of no selection. The results showed seed weight to be a potentially useful selection criterion for root yield. Individual seedling root weight in the greenhouse was not a good predictor of field yield.
The recently released cream-type southernpea cultivar Bettergreen exhibits a unique green cotyledon trait that allows harvest at the near-dry seed stage of maturity without loss of the seed's fresh green color. Progeny tests of plants from the parental, F1, F2, and backcross populations of the crosses `Bettergreen' × `Carolina Cream' and `Bettergreen' × `Kiawah' indicate that the green cotyledon trait is conditioned by a single recessive gene. The results of an allelism test indicate that this recessive gene is not allelic to the gt gene that conditions the green testa trait in the cream-type cultivar Freezegreen. We propose that the new gene be designated green cotyledon and symbolised gc. Seeds containing embryos homozygous for the green cotyledon gene are easily identified. This ability to select in the seed stage should greatly facilitate efforts to backcross the green cotyledon gene into cream-, pinkeye-, and blackeye-type cultivars.
Abstract
Three greenhouse tests to determine the reactions of sweet potato (Ipomoea batatas (L.) Lam.) breeding lines and their respective open-pollinated offspring to 2 species of root-knot nematodes were conducted. Resistances occurred in high frequency to both the southern root knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood) and the Javanese (tropical) root knot nematode (M. javanica (Treub) Chitwood). Reaction to M. incognita was studied in 2 consecutive years with different sets of parental lines using an egg mass index. Estimated heritability (h2) in 1976 was 0.75 ± 0.23 and in 1977 was 0.57 ± 0.37. Three indices of reaction to M. javanica and respective h2 estimates were: Egg mass index, 0.69 ± 0.18; galling index, 0.78 ± 0.19; and necrosis index, 0.72 ± 0.20. Resistances to the 2 species were not correlated, indicating independent inheritance. Development of cultivars with high levels of resistance to each or to both of the above diseases is possible.
Abstract
The gene Cls 1 and the recessive gene cls 2 each conditions a high level of resistance to a leaf spot incited by Cercospora cruenta Sacc. Two Cercospora leaf spot (CLS) resistant breeding lines, CR 17-1-34 (homozygous for Cls 1) and Ala. 963.8 (homozygous for cls 2), were crossed with each other and with each of 3 susceptible cultivars. The F1 and F2 progenies of these crosses, the backcrosses of the CR 17-1-34 × Ala. 963.8 cross, and the parental lines were grown in a field experiment in which a natural CLS epiphytotic was allowed to develop. Cls 1 was completely dominant in all crosses; no evidence was found that either modifying factors or environment had any significant impact on its expression. The cls 2 allele was found not to be a complete recessive under weak epiphytotic conditions, but an incomplete dominant that was highly influenced by the environment when in the heterozygous condition. Cls 1 and cls 2 were neither allelic nor linked.
Abstract
Resistance to diseases of snap beans (Phaseolus vulgaris L.) caused by Rhizoctonia solani was highly heritable and could be easily transferred to lines with high productivity and acceptable quality. Resistance was associated with colored seed. Attempts to obtain white-seeded lines with resistance were not successful because of epistatic effects. The only barrier to the use of cultivars resistant to diseases caused by R. solani is industry refusal of colored-seeded lines, as based on current quality standards. A selection method to obtain near-white-seeded lines is discussed.
Abstract
The inheritance of resistance in cowpea to root knot incited by the root-knot nematodes Meloidogyne incognita (Kofoid & White) Chitwood, M. javanica (Treub.) Chitwood, and M. hapla Chitwood was determined in 3 separate greenhouse experiments. Each seed was inoculated at planting with about 2,000 eggs of the appropriate Meloidogyne species. In Experiment I, plants of parental, F1, F2, and F1 × P1 and F1 × P2 backcross generations of a cross between the resistant cultivar ‘Mississippi Silver’ and the susceptible breeding line CR 18-13-1 were tested for reaction to M. incognita. In Experiment II, plants of parental, some F1, and all F2 generations of a series of crosses involving CR 18-13-1 and the resistant lines ‘Colossus’, ‘Mississippi Silver’, ‘Iron’, and PI 353383 were evaluated for resistance to M. incognita. In Experiment III, plants of parental, F1, and 30 randomly chosen F3 lines of the ‘Mississippi Silver’ × CR 18-13-1 cross were evaluated in separate tests for reaction to M. incognita, M. javanica, and M. hapla. A single dominant gene determined resistance to M. incognita, M. javanica, and M. hapla; the same gene governed resistance in ‘Colossus’, ‘Mississippi Silver’, ‘Iron’, and PI 353383. The gene conditioned a high level of resistance, but it did not confer immunity. Roots of many resistant plants exhibited limited galling and supported some egg production by the parasites. We propose that this gene be designated Root-knot resistance and symbolized Rk.
Abstract
Application of systemic fungicides to sweet potato (Ipomoea batatas (L.) Lam.) increased the total number of healthy seed harvested 50% by increasing pod set, number of seed per pod and the proportion of healthy seed. Insecticides aldicarb and naled gave dramatic responses and increased the number of seedlings obtained per parent plant 2- to 5-fold. Insect damage appeared to be an important cause of low seed set and low seed quality in sweet potato.
Abstract
Two breeding lines of sweet potato [Ipomoea batatas (L.) Lam.] were released in 1975. They possess unusual combinations of disease and insect resistances with other useful characteristics. Both lines originated from mass selection for multiple disease and soil insect resistances in a sweet potato population incorporating a wide gene base. Both lines flower and set seed without any special treatment; traits of particular value in breeding