ARS | Publication request: Inheritance of race and non-race-specific resistance in melon pi 313970 to cucurbit powdery mildew incited by podosphaera xanthii race S.

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 8, 2011
Publication Date: June 1, 2011
Citation: Mccreight, J.D., Coffey, M.D. 2011. Inheritance of race and non-race-specific resistance in melon pi 313970 to cucurbit powdery mildew incited by podosphaera xanthii race S. HortScience. 46(6):1-3.

Interpretive Summary: Powdery mildew disease is a threat to melon (cantaloupe, muskmelon, honeydew, etc.) production anywhere melons are grown. Many strains of the causal fungus are known on melon. Melon plant introduction (PI) 313970 from India is resistant to a new strain of powdery mildew that was first observed in Imperial Valley, California and Yuma, Arizona in 2003. This new strain, designated race S, infects all other known sources of resistance in melon. PI 313970 also exhibits a type of resistance reaction, a water-soaked blister (resistant blister) that appears to be non-race specific and occurs on leaves of plants that otherwise are resistant. Resistance to the race S was controlled by a single recessive gene. Inheritance of the resistance blister reaction was not determined with certainty. Some greenhouse and field data indicate a single recessive gene, but other data are not consistent. Further research is needed to determine with certainty inheritance of the resistant blister reaction. Moreover, research is needed to relate these genes with previously reported genes in PI 313970 and in the other known sources of resistance.

Technical Abstract: A new strain of the cucurbit powdery mildew fungus Podosphaera xanthii, designated race S, first detected on melon (Cucumis melo L.) in the lower desert areas of Yuma, Ariz. and Imperial Valley, Calif. in 2003, overcomes the resistances of all the commonly used melon powdery mildew race differentials. Melon PI 313970 exhibits race-specific resistance (RSR) and non-race-specific resistance (NRSR) manifested as resistant blisters (RB) in response to P. xanthii race S. Inheritance of these two types of resistances to P. xanthii race S was studied in two naturally infected, replicated field tests in Imperial Valley in 2005 and 2009 using the parents, F1, F2, and reciprocal backcross (BC) progenies from the cross PI 313970 (R) x ‘Top Mark’. Race-specific resistance is conditioned by a single, recessive gene. Genetic control of NRSR-RB was not determined with certainty. Single factor and co-segregations in the F2 indicate single, recessive control of NRSR-RB subject to epistasis by the RSR gene: only the double recessive genotype exhibits NRSR-RB. In contrast, the BCR segregated 1 no RB: 1 RB indicative of a single dominant gene. The relationships of these genes with the previously reported recessive and co-dominant genes in PI 313970 for RSR to P. xanthii races 1, 2, 2U.S., 3, 3.5, 4.5 and 5 remain to be determined.