Identification of a New Race and Development of DNA Markers Associated with Powdery Mildew in Melon

Abstract

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Plant Breed. Biotech. 2016 (May) 4(2):225~233 http://dx.ABSTRACT Powdery mildew disease caused by an obligatory parasitic fungus Podosphaera xanthii is a serious problem of melon (Cucumis melo L.) production worldwide. Severity of problem is further associated with emergence of new races over the years. In this study a new race of powdery mildew fungus was discovered from Ibaraki, Japan. The race was different from all other existing races of P. xanthii occurring in Japan. Phenotypic and genetic analysis established the new fungus type as a new race, N5. Ten melon lines were infected with a total of eight fungal races including the new N5 race and it was found that all melon lines had different disease reactions against the new race compared to other seven races. Only four melon genotypes were found resistant out of 42 commercial cultivars and lines were tested. Disease reactions of two sets of F2 populations and one set of backcross population revealed that two separate epistatic gene loci located in two different linkage groups (LG), LG II and LG XII, interact together for the resistant or susceptible reaction of melon lines. A total of six simple sequence repeat (SSR) markers were found polymorphic in melon lines out of 16 tested in response to N5 race. Two different sets of F2 populations between resistant and susceptible melon lines were assessed with two polymorphic SSR markers located in two different groups, LG II and LG XII. SSR genotyping yielded 78% and 94% expected polymerase chain reaction fragments in favor of resistance or susceptibility of F2 populations of CM17187×PMR5 and PMR45×PMR5 of melon lines, respectively.

Identification of Two New Races of Podosphaera xanthii Causing Powdery Mildew in Melon in South Korea

“…This is necessary as the consistency of the races in terms of pathogenicity should be checked prior to determine any new race(s) based on this standard disease causing ability against known differential cultigens. It was observed that the race N1 and race 1 (of all regions) showed same pathogenicity to that of their previous reports ( Hosoya et al, 1999 ; Izumikawa et al, 2009 ; Kim et al, 2016b ; McCreight, 2006 ). This confirmed the consistency of the pathogenicity of the races in differential cultigens to which the uncharacterized races can now be confidently compared.…”

“…Our results identified the isolates of Hadong, Buyeo, Yeongam and Gokseong region as one single race based on their similarity in pathogenicity in the tested differential cultigens. Again, the uniqueness of the pathogenicity of these four isolates compared to that of two known races (tested in this study) and to that of the previous reports against 16 known races ( Hosoya et al, 1999 ; Izumikawa et al, 2009 ; Kim et al, 2016b ; McCreight, 2006 ) indicated it as a new race in Korea; for which the name ‘race KN1’ is proposed. Similarly, the uniqueness of the fungal isolate of Janghueng region indicated it as another new race with a new proposed name, ‘race KN2’.…”

“…When the disease response of eight standard differential cultigens against the collected isolates of four different regions namely, Hadong, Buyeo, Yeongam and Gokseong were compared with that of known races tested in this study and in previous reports ( Hosoya et al, 1999 ; Izumikawa et al, 2008 ; Kim et al, 2016b ; McCreight, 2006 ), it became obvious that none of the isolates showed same pattern of pathogenicity to any of the known races ( Table 1 ). This indicates towards the possibility of these four isolates to be a new race in South Korea and we propose the name ‘race KN1’ for this race as indicated in Table 1 .…”

“… Bardin et al (1999a , 1999b) identified two races of E. cichoracearum and 7 races of S. fuliginea using 10 differential melon genotypes namely, PI124112, PI414723, PMR45, PMR 5, MR-1, WMR29, Edisto 47, Nantais oblong, Védrantais and Iran. Kim et al (2016b) identified a new race, race N5 of powdery mildew of melon based on its unique disease response in ten standard differential cultivars compared to that of against seven known races of P. xanthii (race 1, N1, N2, 5, A, S, O). In the current study, we used eight differential cultigens namely, SCNU1154, PMR 45, WMR 29, PMR 5, MR-1, PI124112, Edisto 47 and PI414723 based on their prior reports of being used in pathogenicity test to identify newly appeared races.…”

“…For identification of the unknown races of P. xanthii , the disease response of a set of eight differential standard melon cultigens namely, SCNU1154, PMR 45, WMR 29, PMR 5, MR-1, PI124112, Edisto 47 and PI414723 were used ( Table 1 ). These cultigens were collected from various sources as indicated in Kim et al (2016b) . Seeds were germinated in plastic pots containing garden soil in a culture room at a controlled day/night temperature of 25/20°C, 16 h day length, 80–120 μmol .…”