Stem cankers on sunflower (Helianthus annuus) in Australia reveal a complex of pathogenic Diaporthe (Phomopsis) species

The identification of Diaporthe (anamorph Phomopsis) species associated with stem canker of sunflower (Helianthus annuus) in Australia was studied using morphology, DNA sequence analysis and pathology. Phylogenetic analysis revealed three clades that did not correspond with known taxa, and these are believed to represent novel species. Diaporthe gulyae sp. nov. is described for isolates that caused a severe stem canker, specifically pale brown to dark brown, irregularly shaped lesions centred at the stem nodes with pith deterioration and mid-stem lodging. This pathogenicity of D. gulyae was confirmed by satisfying Koch’s Postulates. These symptoms are almost identical to those of sunflower stem canker caused by D. helianthi that can cause yield reductions of up to 40 % in Europe and the USA, although it has not been found in Australia. We show that there has been broad misapplication of the name D. helianthi to many isolates of Diaporthe (Phomopsis) found causing, or associated with, stem cankers on sunflower. In GenBank, a number of isolates had been identified as D. helianthi, which were accommodated in several clades by molecular phylogenetic analysis. Two less damaging species, D. kochmanii sp. nov. and D. kongii sp. nov., are also described from cankers on sunflower in Australia

Rhizoctonia bare patch of cereals: An Australian perspective.

Rhizoctonia bare patch disease, caused by Rhizoctonia solani Kuhn AG-8, was first described in Australia in the late 1920s (11,53). Since then, it has been reported in England (7). Canada (1), Scotland (32), and the United States (61). R. solani AG-8 has been confirmed as the causal organism in all locations except Canada

A novel QTL for Septoria speckled leaf blotch resistance in barley (Hordeum vulgare l.) accession PI 643302 by whole-genome QTL mapping

Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii, is one of the most important foliar diseases of barley (Hordeum vulgare L.) in North America. The primary problem caused by this disease is substantial yield loss. The objective of this study was to determine the chromosomal location of SSLB resistance genes in the barley accession PI 643302. A recombinant inbred line population was developed from the cross Zhenongda 7/PI 643302. PI 643302 is resistant while Zhenongda 7 is susceptible to SSLB. The population was phenotyped for SSLB resistance in five experiments in the greenhouse. A linkage map comprising 113 molecular markers was constructed and simplified composite interval mapping was performed. Two QTLs, designated QrSp-1H and QrSP-2H, were found. QrSp-1H was found on the short arm of chromosome 1H (1HS) in all five experiments and showed a large effect against SSLB. Based on the location of QrSp-1H, it is likely the SSLB resistance gene Rsp2. The QTL QrSp-2H mapped to the distal region on the long arm of chromosome 2H (2HL), had a smaller effect than QrSp-1H, and was also detected consistently in all five experiments. A QTL for SSLB resistance in the same region on chromosome 2H has not been reported previously in either cultivated or wild barley; thus, QrSp-2H is a new QTL for SSLB resistance in barley

Amplified fragment length polymorphism and virulence polymorphism in Puccinia hordei

Canadian Journal of Plant Pathology website: http://www.tandfonline.com/loi/tcjp20Puccinia hordei is the causal agent of barley leaf rust. To study the genetic diversity in P. hordei, 45 isolates with diverse virulence patterns and geographical origins were analyzed using amplified fragment length polymorphism markers. Two pathotypes of Puccinia graminis f. sp. tritici and one isolate of P. graminis f. sp. secalis were included in the analysis for comparison. Six primer-pair combinations of amplified fragment length polymorphism were used and a total of 782 polymorphic markers were generated. Cluster analysis showed that P. graminis f. sp. tritici and P. graminis f. sp. secalis were distinctly different from P. hordei. The P. hordei isolates were clustered into five groups: group I contained a single, rare isolate that was virulent on all resistance genes except Rph13 and Rph15 ; group II contained a single isolate found to be virulent on the resistance gene Rph15 ; group III contained 2 isolates; group IV contained 24 isolates, 11 from the United States and 13 from diverse locations around the world; and group V contained 17 isolates, 7 from California, 7 from other states of United States, and 3 from central Europe. The study revealed that molecular diversity in P. hordei can be associated with virulence, but not well with geographic origin

DNA fingerprinting probe specific to isolates of Rhizoctonia solani AG-3

Anastomosis group 3 (AG-3) isolates of Rhizoctonia solani that cause black scurf were recovered from diseased potatoes in Virginia and Lenswood in South Australia. A highly repeated and specific DNA fingerprinting probe, pR3718, prepared from AG-3 isolate R37, hybridized to Southem blots of all AG-3 isolates tested, but had no or very weak reactions with isolates from other anastomosis groups. Genetic variation among the isolates was observed using the fingerprinting probe. Sac I or Hind III restriction endonuclease digests of DNA prepared from 136 AG-3 isolates revealed 38 fingerprint patterns, each containing 12-19 Sac I or Hind III fragments. Because the pR3718 clone recognizes a DNA sequence with a high number of copies per genome and appears to be specific for AG-3 isolates of Rhizoctonia, it has the potential to be used as a diagnostic tool to study the epidemiology, genetic diversity and population dynamics of this important plant pathogen