Cucurbit Genetics Cooperative Report 14:56-58 (article 21) 1991
A.A. Hassan, H.H. Al-Masri, U.A. Obaji, M.S. Wafi, N.E. Quronfilah, and M.A. Al-Rays
Faculty of Agricultural Sciences, U.A.E University, Al-Ain, U.A.E. and Department of Agriculture and Animal Production, Al-Ain, U.A.E
Cucurbits are the most important group of vegetables grown in the U.A.E. their production has been seriously threatened, however, by a yellow-stunting disorder (YSD) caused by a new virus of the closterovirus-like group similar to lettuce infectious yellows virus (LIYV) (2). The tobacco whitefly, Bemisa tabaci Genn. is thoughtto be the vector of this virus which was observed in a 15 out of 6 affected samples examined by electron microscopy as long flexuous filamentous particles (3).
All attempts made locally to control the disorder through the control of whiteflies failed. The use of spunponded polysters and polypropylene plant covers for about 35 days (until flowering) was promising in controlling the disorder (4). However, this practice has not gained acceptance among U.A.E. farmers, yet; probably due to its high cost. At present, none of the tested commercial melon (Cucumis melo L.) cultivars were found resistant to this by the Department of Agriculture and Animal Production in Al-Ain (5) in melon cvs. ‘Caribe’, ‘Maggar Kings’, ‘Muskotaly’, ‘Midstar’, and ‘Rock Sweet’. The use of resistant cultivars would be the simplest and most eficient method of controlling this disorder. Hence, the objective of this study was to search for sources of resistance to the YSD in a large collection of domestic and wild C. melo accessions.
Nine hundred seventy five wild and domestic C. melo accessions were evaluated for resistance to the YSD under field conditions in Al-Ain, U.A.E. in the spring and autumn planting of 1988 and 1989. The 1988 spring and autumn trials included 488 U.S.D.A. C. melo plant introductions (PIs) and 7 commercial melon cultivars that were recommended by the Department of Agriculture and Animal Production for re-evaluation. Four of these cultivars were previously reported to be only slightly susceptible to the disorder (5). A different lot of 480 PIs were evaluated in the 1989 spring trial. Twenty-five of the most promising PIs in these trials (12 of the 1988 spring and autumn trials and 13 of the 1989 spring trials) were selected for re-evaluation in the 1989/1990 autumn trial in comparison with the susceptible cultivar ‘Ananas’. Seeds of PIs evaluated were kindly provided by the U/S.D.A. through Dr. Raymond Clark (Plant Introduction Station, Ames, Iows), while seeds of commercial cultivars were provided by local seed dealers.
Field seed sowing was during the third week of March for the spring trials and the first week of September for the fall trials in both years of the study. After thinning, individual plants were spaced 50 cm apart in rows 11.5 m-wide. Each accession was assigned to one 8.0 m row in the first, second and third trials and to 3-6 similar rows in a completely random design in the last (1989/1990 autumn) trial. The number of plants evaluated of each accession were as follows: 3-16 (x = 7.7, Sd = 2.98, mode = 4) in the 1988/1989 autumn trial, 3-14 (x = 9.8, Sd = 2.43, mode = 10) in the 1989 spring trial, and 2-6/replicates in the 1989/1990 autumn trial.
Natural infection by the YSD was enhanced by placing heavily whitefly-infested melon plants showing severe symptoms of the disorder nearby the evaluated plants one week after germination. No pesticides were applied to maintain a high population of viruliferous whiteflies which were continuously observed on the plants in all trials. In the 1988 spring trial, each accession was classified as either resistant (R) or susceptible (S). The former group did not show any visible symptoms of the YSD on any of the plants when they were examined 8 weeks after seed sowing. In other trials, each plant was given a diseased score 8 and/or 10 weeks after seed sowing according to the following scale: 1, no symptoms; 2, slight; 3, moderate; and 4, severe symptoms. Individual plant ratings for each accession were added and divided by the number of evaluated plants toi obtain the corresponding mean disease scores (MDS). Then, accessions were classified as either R, slightly susceptible (SS), moderately susceptible (MS), or highly susceptible (HS) when their MDSs were 1.0-1.5, 1.6-2.5, 2.6-3.5, and 3.6-4.0, respectively. In the 1989 spring trial, accessions classified as R or SS 8 weeks after seed sowing were re-evaluated 2 weeks later. The second readings were assigned to the respective accessions which were signaled out in the delayed symptoms development category.
Based on the final (1989.1990 autumn) trial (Table 1), none of the accessions svaluated were found highly resistant or immune. Fourteen PIs were significantly different from cv. ‘Ananas’. in mean disease score (MDS) 8 weeks after seed dowing, 9 of which were different at the 1% level; but the number diminished to 5 PIs when disease rating was repeated 2 weeks later, with only PI 403994 remaining highly significantly different from “ananas’. The others were PIs 2554778, 2922007, 381766, and 390452, PI 403994, the best performing accession in these trials, was given MDSs of 1.68 and 2.95 (or was classified as slightly and moderately susceptible) at 8 and 10 weeks after seed sowing, respectively; while ‘Ananas’ was rated 3.77 and 4.00 at the 2 dates, respectively.
In line with previous reports, cultivars ‘Jupiter’ and ‘Muskotaly’ showed only slight symptoms of the disorder, while ‘Caribe’, ‘Midstar’ and ‘Rick Sweet’ were rated 8 weeks after the seed sowing as slightly susceptible.
Table 1. Response of selected C. melo accessions re-evaluated in the 1989/1990 autumn planting to the yellow stunting disorder.
Response in previous trials |
No. of replicates |
Mean disease score after weeks indicated from seed sowing |
||||
Accessions (PI) |
Spring 1988z |
Autumn 1988z |
Spring 1989z |
8 weeksy |
10 weeksy |
|
| 164797 | R | HS | – | 3 | 3.66 n.s | 3.83 n.s. |
| 179680 | R | R | – | 4 | 3.48 n.s. | 3.88 n.s. |
| 179922 | S | MS | – | 4 | 2.66 ** | 4.00 n.s. |
| 211116 | S | SS | – | 6 | 2.50 ** | 3.85 n.s. |
| 214154 | R | MS | – | 5 | 3.49 n.s. | 3.90 n.s. |
| 222984 | R | MS | – | 6 | 3.27 n.s. | 4.00 n.s. |
| 229555 | R | – | – | 3 | 2.18 ** | 3.77 n.s. |
| 255478 | R | – | – | 3 | 1.33 ** | 3.40 *. |
| 255953 | – | – | – | 6 | 2.57 ** | 3.87 n.s.. |
| 288233 | – | – | ss-d | 4 | 2.45 ** | 3.88 n.s. |
| 292007 | – | – | ss-d | 5 | 2.74 ** | 3.35 * |
| 323498 | – | – | ss-d | 6 | 3.28 n.s. | 4.00 n.s. |
| 353451 | R | – | HS-d | 5 | 2.56 ** | 3.97 n.s. |
| 378062 | – | – | – | 4 | 2.80 * | 4.00 n.s. |
| 378063 | R | – | MS-d | 5 | 3.06 n.s. | 4.00 n.s. |
| 378064 | – | MS | – | 6 | 2.75 * | 3.90 n.s. |
| 381762 | R | – | ss-d | 6 | 3.36 n.s. | 3.93 n.s. |
| 381772 | – | HS | ss-d | 6 | 3.38 n.s. | 3.97 n.s. |
| 381766 | – | – | ss-d | 6 | 2.30 ** | 3.50 * |
| 381800 | – | – | ss-d | 6 | 3.05 n.s. | 3.92 n.s. |
| 381802 | – | – | ss-d | 6 | 3.13 n.s. | 3.92 n.s. |
| 385966 | – | – | MS-d | 5 | 3.27 n.s. | 4.00 n.s. |
| 390452 | – | – | R-d | 6 | 2.51 ** | 3.52 * |
| 401624 | – | – | – | 5 | 2.97 * | 3.85 n.s. |
| 403994 | – | – | 6 | 1.68 ** | 2.95 n.s. | |
| cv. Ananas’ | – | – | 6 | 3.77 (control) | 4.00 (control) | |
zR, resistant; S, susceptible; SS, slightly susceptible; MS, moderately susceptible; HS, highly susceptible; the letter ‘d’ refers to delayed symptoms’ development at 10 weeks after seed sowing.
yL.S.D. between accessions with 3, 4, 5, and 6 replications and the control (cv. ‘Ananas’) were, respectively, as follows:
P = 0.05 at 8 weeks : 0.91, 0.83, 0.78, and 0.74;
P = 0.01 at 8 weeks : 1.20, 1.10, 1.03, and 0.98;
P = 0.05 at 10 weeks : 0.49, 0.44, 0.42, and 0.40;
P = 0.01 at 10 weeks : 0.64, 0.59, 0.55, and 0.53.
Accessions were either not significant (n.s.), significant (*), or highly significant (**) from the control.
Literature Cited
- Hassan, A.A. and H.H. Al-Masri. 1990. Preliminary evaluation of cucurbits for resistance to the yellow stunting disorder. Emirates J. Agr. Sci. 2:
- Hassan, A.A. and J.E. Duffus. 1990. A review of a yellowing and stunting disorder of cucurbits in the United Arab Emirates. Emirates J. Agr. Sci. 2:
- Lecoq, H. 1986. Report of a visit to the United Arab Emirates to study a yellowing and stunting disorder of cucurbit crops. I.N.R.A., Montfavet, France. (Available at the Dept. of Agr. & Animal Prod., Box 1004, Al-Ain, U.A.E.).
- Ministry of Agriculture and Fishery, U.A. E. 1987. A report on the decline of melon and watermelon crops. Part I (In Arabic). Northern Agr. Region. (Available at the Minst. Agr. & Fish., Box 1509, Dubai, U.A.E.).
- Salih, M.E. 1988. Role of the Department of Agriculture and Animal Production in past, present and future research in the area of plant production (In Arabic). In ‘Future of Agriculture in the United Arab Emirates: A Developmental Perspective, pp. 77-97. Proceedings of a Symposium Held at the Faculty of Agricultural Sciences, U.A.E. University, Al-Ain.