3.4.62
LABORATORY ASSESSMENT ON COMPARATIVE SUSCEPTIBILITY OF POTATO TUBERS OF SOME ADVANCED WILD CLONES (PHUREJA) TO FUSARIUM DRY ROT (F. SOLANI AND F. SULPHUREUM)

A MORTAZAVI-BAK1 and M NASR-ESFARANI2

1Seeds and Seedlings Improvement Division, and 2 Plant Pests and Diseases Research Division, Agriculture Research Center, Esfahan, PO Box 81785-199, Iran

Background and objectives
Variations in susceptibility of potato (Solanum tuberosum) cultivars to Fusarium dry rot has been long known [1]. Many cultivars reacts differently to F. sulphureum and F. solani, even when similar methods of inoculation and incubation have been used [1]. In view of these, thus the reaction of several advance clones (Phureja) to inoculation of F. sulphureum and F. solani was studied, as routine screening of breeders clones for resistance to dry rot.

Materials and methods
Thirty five wild clones (Phureja) were taken from the Scotish Crop Research Institute (SCRI) and kept in a frost-free store at 6-10C. The cultures of the two pathogens were already inoculated to the susceptible cultivar (to ensure that they remained pathogenic), out of which the fresh isolates were obtained from the same sources. The inoculum was prepared by growing the isolates on PDA and then were mixed with sand (1:1). The tubers of each clone were washed and left overnight, then after individually wounded approximately half way between the rose and heel ends by a cork-borer of 5 mm in diameter to the depth of 10 mm filled with the inoculum. The inoculated tubers were placed in plastic baskets separately and kept at 1010C and 70-80% humidity to promote the dry rot development. After about 8 weeks, the extent of the disease was determined by cutting the tubers through the wounds, using scoring scale (0,1/16,1/8,1/2 and >1/2), in which the number of tubers in each class was multiplied by 0, 1, 3, 6, 12 or 24, respectively, and the mean score on the 0-24 scale was calculated for each clone separately [1, 2].

Results and conclusions
The results indicated that there are certain variation between the tested wild clones as far as the extent of the disease development for every species is concerned. This type of variations have been observed by several workers only in potato cultivars [1], but not in wild clones (Phureja) so far. The mean scores of dry rot showed that, there are wild clones (DB109-55, DB184-56, H2B20-26, HB34-45) which are rather immune (0) and also (BIP-12; B425-61, 76,86; HIB145-13) highly susceptible (24), where the rest were intermidiate with various degrees of response to F. solani. The wild clones also reacted differentialy but none were immune to F. sulphureum such as H23-34(45), H2B1-120(6) with the mean scoring of 3, followed by B42P-28 of 4.4, DB264(32) of 5 and B42P-54 of 6 and highly susceptible such as B42S-76, B42S-86, B42S-105, DB200-20, DB271-2 and XBX33-45 with 24. It can be concluded that, not only are there differences in ranking orders in response to F. solani and F. sulphureum independently, though the similar method of inoculation was employed, but also there are certain advance wild clones (Phureja) for resistance to dry rot.

References
1. Wastie RL, Stewart HE and Brown J, 1989. Potato Research 32, 49-55.
2. Wastie RL and Bradshaw JE, 1995. Potato Research 38, 345-351.