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  • Author or Editor: Claude E. Thomas x
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Abstract

MR-1 is a monoecious muskmelon (Cucumis melo L.) breeding line that was developed the by USD A to provide breeders and seedsmen with a source of high levels of resistance to both downy mildew, incited by Pseudoperonospora cubensis (Berk, and Curt.) Rostow., and powdery mildew, incited by Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll. It is resistant to 2 undesignated races of downy mildew and to races 1,2, and 3 of powdery mildew.

Open Access

Abstract

‘Cinco’ is a multidisease resistant muskmelon (cantaloupe), Cucumis melo L., with excellent keeping qualities, good appearance, and delicate sweet taste. It is highly resistant to watermelon mosaic virus 1 (WMV-1); downy mildew, Pseudoperonospora cubensis (Berk. & Curt.) Rostow.; races 1 & 2 of powdery mildew Sphaerotheca fuliginea (Schlect. ex Fr.) Poll.; and Alternaria leaf-blight Alternaria cucumerina (Ellis & Everh.) Elliot. It was developed in south Texas where these fungus diseases occur regularly in epiphytotic proportions. The fruit keeps well for long-distance shipping. The size is that preferred by local market and home garden growers.

Open Access

Evaluations for resistance against race 2 of downy mildew, incited by Peronospora parasitica, were conducted on 240 U.S. Plant Introductions (PI) classified as Brassica oleracea var. botrytis (consists of both broccoli and cauliflower types). Plants were inoculated at the two-expanded leaf stage with 5.0 × 103 sporangia per ml. Inoculated plants were incubated in a dark 16C dew chamber for 24 hr and were then placed in a 22C growth chamber with a 12-hr photoperiod. On the 7th day after inoculation, plants were returned to the dew chamber for 30 hr and ratings for downy mildew reaction phenotypes were made at 9 days postinoculation on a 0-9 scale of increasing disease severity. A disease index (DI) was calculated for each entry. Based on the DI, no PI entries were highly resistant. PI entries 181860, 188562, 204765, 204768,204772,204773, 204775,204779,241612, 264656,291567,373906, and 462225 were moderately resistant. (DI of 3.1-5).

Free access

Evaluations for resistance against race 2 of downy mildew, incited by Peronosporu parasitica Pers. ex Fr., were conducted on 325 U.S. Plant Introductions (PI) classified as Brassicu oleracea var. capitata L. (cabbage). A disease index (DI) was calculated for each entry. In 77 of the tested PIs, from 2% to 100% of the plants had reaction phenotypes ≥ 3. The DIs for 24 PIs were significantly lower than the DI for the most resistant cabbage control, `Headstart' (DI = 5.9). Eight of these PIs were highly resistant, because all plants had a reaction phenotype ≥ 3. However, most of these eight are apparently misclassified as B. oleracea var. capitata.

Free access

Field evaluations for resistance against downy mildew, incited by Pseudoperonospora cubensis [(Berk. and Cart.) Rostow], were conducted on 942 U.S. Plant Introductions (PI) of Cucumis melo L. (melon). A disease index (DI) was calculated for each entry. Based on DI, PI 124112 was highly resistant (DI = 3.7), and PIs 124111, 122847, 124210, 145594, and 165525 were resistant (DI = 3.0, 2.8, 2.6, 2.7, and 2.5, respectively). PIs 124111 and 124112 had one or more plants that exhibited a highly resistant reaction type (RT 4). Resistant (RT 3) plants were identified in 31 accessions, and 49 accessions bad moderately resistant (RT 2) plants.

Free access

A genetic linkage map was previously constructed for watermelon using a wide testcross population [{Plant Accession Griffin 14113; Citrullus lanatus var. citroides (L.H. Baiely) Mansf.} × the watermelon cultivar New Hampshire Midget; NHM {(Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus)} × United States Plant Introduction (PI) 386015 {Citrullus colocynthis (L.) Schrad.}]. One-hundred forty-six markers [randomly amplified polymorphic DNA (RAPD), intersimple sequence repeat (ISSR), amplified fragment length polymorphism (AFLP), and sequence-related amplified polymorphism (SRAP) markers] unique to NHM and representing different linkage groups on the map were tested for polymorphism among 24 watermelon cultivars limited in genetic diversity. Five (9.4%) of 53 RAPD, six (40.0%) of 15 ISSR, 30 (81.0%) of 37 AFLP, and 33 (80.5%) of 41 SRAP markers tested produced polymorphism among the 24 cultivars. The polymorphic markers used in this study are scattered throughout the watermelon genome. However, a large number (19 of the 30) of AFLP markers clustered on one linkage group on the map. The SRAP markers proved to be most effective in producing polymorphism and in representing different linkage regions of watermelon genome. The polymorphic markers represent all 10 large linkage groups and five of the nine small linkage groups (altogether 15 of 19 linkage groups) of the genetic linkage map constructed so far for watermelon. These polymorphic markers can be useful in DNA fingerprinting of cultivars, in testing seed purity of breeding lines, and in identifying triploid (seedless) hybrid watermelons derived from crosses between closely related tetraploid and diploid lines.

Free access

Abstract

Muskmelon (cantaloupe), Cucumis melo L., lines W1, W3, W4, W5, and W6 released by the Southern and Northeastern Regions, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture represent multidisease-resistant advanced breeding lines with high-quality attributes suited to the development of cultivars for long-distance shipping as well as for small farm and home garden production. They were selected under severe epiphytotie conditions in South Texas for resistance to downy mildew, Pseudoperonospora cubensis (Berk.) Rostow.; powdery mildew, Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll.; Alternaria leaf-blight, Alternaria cucumerina (Ell. & Ev.) Elliot; and watermelon mosaic virus 1 (WMV-1). In extensive, replicated, repeated field studies, these lines were consistently found to possess a high level of resistance to all of these diseases, enabling production of a marketable crop under severe disease stress, often without application of fungicides. W4, W5, and W6 exhibit a higher level of resistance to dow ny mildew and Alternaria leaf-blight than do the more moderately resistant W1 and W3 lines. All 5 lines are highly resistant to powdery mildew and have excellent resistance to natural infections of WMV-1.

Open Access

Two hundred sixty-six Citrullus lanatus (Thumb.) Matsum. & Nakai accessions (Plant Introductions and named cultivars) were tested against a race 2 Sphaerotheca fuliginea (Schlechtend.: Fr.) Pollacci isolate to evaluate for resistance to powdery mildew disease. Growth room-grown seedlings were artificially inoculated with conidia from watermelon host leaves at 2-day intervals from the appearance of the first true leaf until test results data were taken, when the second true leaf was fully expanded. Plants were evaluated on a 1 to 9 scale of increasing disease severity. Disease indices (DIs) were calculated as weighted averages for each entry. All genotypes with resistant plants (powdery mildew rating 1 to 3) were reevaluated in a replicated test of 3 replications of 10 plants each. Disease indices were again calculated. Twenty-two plant introductions (PIs) and one named variety displayed intermediate resistance to powdery mildew in the replicated test with DIs ranging from 5.0 to 6.0.

Free access

Downy mildew, incited by the biotrophic fungal parasite, Peronospora parasitica (Pers. Fr.) Fr., is one of the most destructive diseases of broccoli (Brassica oleracea L., Italica Group) and other related crop species throughout the world. Cultivation of resistant cultivars is the most desirable control method because it provides a practical, long-term, and environmentally benign means of limiting damage from this disease. The commercial hybrid cultivar, Everest, has been shown previously to contain a high level of downy mildew resistance. Doubled-haploid (DH) lines developed from that hybrid were also shown to exhibit a similar, high level of resistance at the three- to four-leaf stage. To determine the mode of inheritance of this true leaf resistance, the resistant DH line was crossed to a susceptible line (derived from `Marathon') to produce an F1 hybrid. Subsequently, F2 and backcross (BC) populations were developed from the hybrid. In addition, a DH population of ≈100 lines was developed from the same F1 used to create the F2 and BC. All populations were evaluated for response to artificial inoculation with P. parasitica at the three- to four-leaf stage. F1 plants were resistant like the resistant parent and F2 populations segregated approximately nine resistant to seven susceptible. Using the resistant parent as recurrent parent, BC populations contained all resistant plants, while the BC to the susceptible parent fit a 1 resistant: 3 susceptible segregation ratio. These results can be explained by a model with two complementary dominant genes. This model was confirmed by the DH population that segregated ≈1:3, resistant to susceptible. Due to the dominant nature of this resistance, controlling genes should be easily incorporated into F1 hybrids and used commercially to prevent downy mildew.

Free access

Broccoli (Brassica oleracea L. Italica group) breeders routinely use anther or microspore culture to produce dihaploid (diploid), homozygous lines. During the culture process, polyploidization occurs and diploid regenerants can result. However, polyploidization may not occur at all, or it may involve a tripling or quadrupling of the chromosome complement. Thus, regenerated populations must be screened to identify the diploids that are the regenerants most likely to set seed and serve as inbred lines. DNA flow cytometry has proven a useful procedure for determining ploidy of anther derived regenerants. This study was undertaken to evaluate the effect of leaf age and sampling procedures on ploidy determination via flow cytometry. Anther-derived plants were analyzed at a four- to five-leaf stage (transplant stage) and at time of heading (mature plant stage). In addition, leaves were sampled on a given date and stability of the flow cytometry preparations was evaluated over 7 days. Lastly, the stability of ploidy readings of leaves stored at 4°C was examined over a 7-day period. In only one case out of 123 comparative assays did leaf age affect ploidy determination. For that exception, a haploid at transplant stage was a diploid at the mature plant stage. Flow cytometry preparations and also leaves stored at 4°C gave consistent ploidy determinations up to four days after preparations were made or tissue was refrigerated, respectively. These results indicate that broccoli breeders can make flow cytometry preparations on site and send them offsite for flow cytometry analysis. Alternatively, leaves could be refrigerated, sent offsite, and then prepared and analyzed at another location.

Free access