Cucurbit Genetics Cooperative Report 20:30-31 (article 14) 1997
E.A. Ahmed, A.E. El Jack and Y.F. Mohamed
University of Gezira, P.O. Box 20, Wad Medani, Sudan
Snake melon (Cucumis melo var. flexuosus) is a popular vegetable in Sudan, consumed fresh in salad and also in pickles. Powdery mildew is one of the most important limiting production factors, specifically during winter in Sudan (1). This project aims at breeding a resistant snake melon cultivar to powdery mildew, since there are presently no resistant cultivars.
A field study was conducted during Oct 1996 to Jan 1997 at the University Experimental Farm. Material tested included PI 414723 (resistant), local cv. Shendi (susceptible), F1 (‘Shendi’ X PI 414723), BC1 (‘Shendi’ X F1) and the F2 population. Differential hosts shown in Table 2 were planted at the same time with the tested material. The plants were inoculated fifteen days after planting by spraying a spore suspension. A rating scale of 1 to 9 (1 = high susceptibility and 9 = high resistance) was used. The powdery mildew was examined both in the laboratory using conidial structures and germination of spores, and on differential hosts in the filed.
The results (Table 1) indicated that ‘Shendi’ was highly susceptible (PMR=1), PI 414723 was resistant (PMR=9) and their F1 was intermediate (PMR=6.2). The F2 showed segregation with about 7.6% having the level of resistance of the PI 414723. The BC1 also showed segregation with 33% having the level of resistance of the F1. This indicated partial dominance of the resistance. Due to the production of fibrosin bodies in the conidia, arrangement of conidia in chains at the apex of the conidiophores and through the lateral germination of germtubes (2), the causal agent was identified as Sphaerotheca fuliginea. This was further confirmed by the known reaction of the differential hosts (Table 2). Since ‘Nantais oblong’ was not infected, Erysiphe cichoracearum was ruled out as a causal agent.
In conclusion, resistance to powdery mildew can be transferred into ‘Shendi’ through backcrosses with selfing. Seasonality of race prevalence should be considered in the breeding programs as race 1 prevails during the warmer time of the season and race 2 during the cooler part of the season (1).
Table 1. Distribution of rating for powdery mildew resistance (PMR) of the different lines and crosses tested.
Number of plants in each disease rating classz |
|||||||||||
Line or Cultivar |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
Total no. of plants |
Mean |
| Shendi | 200 | – | – | – | – | – | – | – | – | 200 | 1.0 |
| PI 414723 | – | – | – | – | – | – | – | – | 25 | 25 | 9.0 |
| F1 (Shendi x PI 414723) | – | – | – | 4 | 8 | 8 | – | – | – | 20 | 6.2 |
| F2 (Shendi x PI 414723) | 22 | – | 25 | – | 30 | – | 22 | – | 19 | 118 | 4.8 |
| BC (Cv. Shendi x F1) | 35 | – | 26 | – | 19 | 1 | 10 | – | – | 91 | 3.2 |
z 1 = highly susceptible, 9 = highly resistant
Table 2. Observed reaction of differential hosts to infection of powdery mildew in the filed in 1996-97.
Differential hosts |
||||||||
Iran H |
Nantais oblong |
PMR 45 |
WMR 29 |
PMR 1 |
PMR 5 |
PI 414723 |
PI 124112 |
|
| Reaction type | Sz | S | S | R | R | R | R | R |
z R = resistant, S = susceptible
Literature Cited
- Mohamed, Y.F., M. Bardin, P.C. Nicot and M. Pitrat. 1995. Causal agents of powdery mildew of cucurbits in Sudan. Plant Disease 79(6): 634-636.
- Zaracovitis, C. 1965. Attempts to identify powdery mildew fungi by conidial characters. Trans. Br. Mycol. Soc. 48: 553-558.