Genetic variation in Zantedeschia spp. (Araceae) for resistance to soft rot caused by Erwinia carotovora subsp. carotovora

Bacterial soft rot caused by Erwiniacarotovora subsp. carotovora is amajor disease in Zantedeschia spp.,particularly in cultivars from the sectionAestivae. The disease can partiallybe controlled by cultivation measures, so acombination with resistant cultivars couldeffectively protect the crop. However,resistant commercial Aestivaecultivars are not available yet. By meansof a recently developed non-destructiveresistance test, variation inaggressiveness was observed among fiveisolates of Erwinia carotovora subsp.carotovora without interactionsbetween the isolates and three Zantedeschia accessions. Within elevenaccessions of Z. aethiopica,variation was observed from almost completeto moderate resistance, while theZ. odorata accession was susceptible.All 21 Aestivae cultivars weresusceptible. Within the Aestivaespecies, Z. elliotiana and Z.pentlandii were also susceptible, butwithin twelve accessions of Z.albomaculata, as well as in six accessionsof Z. rehmannii, variation was foundfrom susceptible to moderately resistant.Hence, new sources of resistance wereidentified that show good potentials forresistance breeding.     

Identification of Rfd1, a novel restorer-of-fertility locus for cytoplasmic male-sterility caused by DCGMS cytoplasm and development of simple PCR markers linked to the Rfd1 locus in radish (Raphanus sativus L.)

Previously, novel cytoplasmic male-sterility (CMS) caused by DCGMS cytoplasm was discovered in radish (Raphanus sativus L.) introduced from Uzbekistan. We performed extensive progeny tests and identified two fertility restorer lines (‘R171’ and ‘R121’) for this new CMS. Two F₁ hybrid populations were self-pollinated and backcrossed to produce F₂ and BC populations. Inheritance patterns of male-sterility in segregating populations varied depending on paternal lines. Segregation of male-sterility in F₂ populations originating from the cross between MS19 and R121 showed that a single locus was involved in fertility restoration. However, populations originating from the cross between MS15 and R171 showed the involvement of more than one restorer-of-fertility genes. The single fertility restorer locus identified in the cross between MS19 and R121 was designated Rfd1 locus. Bulked segregant analysis was performed using RAPD and AFLP, which identified one marker each. Both RAPD and AFLP markers were converted into simple PCR-based co-dominant markers after their isolated flanking sequences were analyzed. Indels 773-bp and 67-bp in length were identified between two Rfd1 allele-linked flanking sequences of the RAPD and AFLP fragments, respectively, then utilized to develop simple PCR markers. In addition, we prove that the newly identified Rfd1 locus is independent of the Rfo locus, another radish fertility restorer for CMS caused by Ogura cytoplasm.