ارزیابی مقاومت نسبی 30 ژنوتیپ پاکوتاه محلب به چهار گونه‌ی فیتوفتورا در گلخانه و باغ

Introduction:
The best cherry rootstock for Iranian nurseries and orchards is Prunus mahaleb (L.) Mill. Mahaleb is tolerant to lime-induced iron chlorosis and zinc deficiency. It is a good rootstock on light, calcareous soils and arid climates in Iran but sensitive to Phytophthora. Iran represents a significant source of germplasm of different fruit species, especially for those from the genus Prunus. Collection and research on P.mahaleb was initiated at the Horticultural Department of Khorasan Razavi Agriculture and Natural Resources Research and Education Center in 1997 for mahaleb cherry rootstock. Some researchers have reported pathogenicity of Phytophthora species (Banihashemi and Sartipi, 2004; Wilcox and Mircetich, 1985; Exadaktylou and Thomidis, 2005; Tomidis et al., 2008). This study was conducted to evaluate the susceptibility of 30 selected dwarf Mahaleb genotypes to P.nicotianae, P.citricola, P.cactorum and P. citrophthora under greenhouse and orchard conditions.

Material and methods:
In this study, the response of 30 selected dwarf Mahaleb genotypes (188, 171, 165, 162, 161, 155, 139, 136, 131, 120, 106, 104, 101, 100, 90, 194, 195, 199, 200, 224, 228, 247 , 249, 265, 266, 267, 268, 270, 272, 277) to disease caused by four species of the fungus Phytophthora root and crown rot were investigated under greenhouse and orchard conditions. Greenhouse experiments were performed based on Ribeiro and Baumer, 1977 and modified it by Feichtenberger et al., 1984. For evaluation the index disease was performed based on the method of Broadbent and Gollnow 1992. Orchard terials was laid out in the Toragh research station in Mashhad. Evaluation of genotypes and contamination based on Tomidis, 2001 was performed by measuring the area of necrosis.

Results and discussion:
In evaluating the reaction of young seedling dwarf mahaleb genotypes to four Phytophthora species under greenhouse conditions, results showed that four species of Phytophthora pathogens on all mahaleb genotypes but P.citricola, P.cactorum showed disease severity than P.citricola, P. nicotianae. In response assessment test seedlings in the greenhouse genotypes Mahaleb highest rate of infection to P.cactorum in genotype 277 and the lowest index of disease severity showed in genotypes 100, 188, 199, 200, 224 and 266, respectively. The highest and lowest number of leaves was counted on 199, 272 and 277 respectively. The least and highest shoot dry weight were related to 277 and 100 genotype respectively. The maximum and minimum disease severity to P.citrophthora revealed in 265 and 265, 100, 188, 194, 199 genotypes, respectively. The highest and lowest number of leaves was counted on 188 and 249 respectively. The least and highest shoot dry weight were related to 249 and 100genotype respectively. The least and highest root dry weight was measured on 265 and 100 genotype, respectively. In response assessment test seedlings in the greenhouse genotypes Mahaleb highest rate of infection to P.citricola in genotype 265 and the lowest index of disease severity showed in genotypes 100, 162, 171, 188, 199, 200,224, respectively. The highest and lowest number of leaves were counted on 100and 277, 272 respectively. The least and highest shoot dry weight were related to 272 and 100 genotype respectively. The least and highest root dry weight were related to 277 and 100 genotype respectively. The highest rate of infection to P.nicotianae in 120 genotype and the lowest index of disease severity were related to the genotype of 188 and 199. The highest number of leaves in genotype No.100 and the lowest number of leaves were belonging to genotypes 272 and 277, respectively. The least and highest shoot dry weight were related to 247 and 100 genotype respectively. The least and highest root dry weight were related to 265 and 100 genotype respectively. The results of the assessment of the two year old seedlings mahaleb genotypes under orchard conditions showed that four Phytophthora species had different degrees of disease symptoms. Phytophthora species in their ability to create the symptoms are different. The lowest level of necrosis is created by P.cactorum. The highest and lowest levels of necrosis of P.cactorum were measured in 267 and 162 genotypes, respectively. In P. citrophthora, the highest and lowest levels of necrosis were measured in 277 and 188 genotypes, respectively. The highest and lowest levels of necrosis of P. nicotianae were measured in 272 and 188 genotypes, respectively.

Conclusion
The results of the assessment Mahaleb genotypes to four species of Phytophthora in the orchard showed that the lowest level of tissue necrosis in genotypes of 106, 139, 162, 188, 195, 224, 266 and 270, respectively. Finally our results revealed that P.citricola, P.cactorum were pathogenic Phytophthora species and three mahaleb genotypes (266, 224 and 188) had highest potential resistance to P. nicotianae, P.citricola, P.cactorum and the P.citrophthora respectively.