Isolates Of Anastomosis Groups Research Articles

Sequence variation of the rDNA ITS regions within and between anastomosis groups in Rhizoctonia solani.

Sequence analysis of the rDNA region containing the internal transcribed spacer (ITS) regions and the 5.8s rDNA coding sequence was used to evaluate the genetic diversity of 45 isolates within and between anastomosis groups (AGs) in Rhizoctonia solani. The 5.8s rDNA sequence was completely conserved across all the AGs examined, whereas the ITS rDNA sequence was found to be highly variable among isolates. The sequence homology in the ITS regions was above 96% for isolates of the same subgroup, 66-100% for isolates of different subgroups within an AG, and 55-96% for isolates of different AGs. In neighbor-joining trees based on distances derived from ITS-5.8s rDNA sequences, subgroups IA, IB and IC within AG-1 and subgroups HG-I and HG-II within AG-4 were placed on statistically significant branches as assessed by bootstrap analysis. These results suggest that sequence analysis of ITS rDNA regions of R. solani may be a valuable tool for identifying AG subgroups of biological significance.

RFLP analysis of the PCR-amplified 28S rDNA in Rhizoctonia solani

RFLP analyses of a portion of the 28S rDNA gene region were conducted by using four restriction endonucleases for 57 isolates of 13 intraspecific groups (ISGs) representing 7 anastomosis groups (AGs) ofRhizoctonia solani. Variations in the PCR-amplified rDNA products and the polymorphisms on digestion with restriction enzymes (BamHI,HaeIII,HhaI andHpaII) were observed among three AGs, AG 1, 2 and 4. These differences were also conserved among some ISGs of AG 1 and AG 2. Among ISGs of AG 1, the pattern of rDNA fragments of AG 1-IA obtained by digestion withHpaII was significantly different from those of AG 1-IB and IC. Such difference in the fragment pattern was also observed among AG 2-1, 2-2 IIIB and 2-2 IV by the digestion withHhaI andHpaII. A dendrogram derived from the restriction enzyme data showed that ISGs from AG 1 and AG 2 can each be subdivided into distinct groups, those are distantly related to the majority isolates of the other AGs.

Polymorphism of genes coding for nuclear 18S rRNA indicates genetic distinctiveness of anastomosis group 10 from other groups in the Rhizoctonia solani species complex

DNA polymorphism in the 18S nuclear rRNA gene region was investigated by using 11 restriction endonucleases for 161 isolates of 25 intraspecific groups (ISGs) representing 11 reported anastomosis groups (AGs) of Rhizoctonia solani. A PCR-based restriction mapping method in which enzymatically amplified DNA fragments and subfragments were digested with one or two restriction enzymes was employed. Four types of DNA restriction maps of this region were constructed for these 25 ISGs. Map type I of the 18S rDNA region was represented by isolates of a majority of R. solani ISGs. Map types II and III, represented by ISG 2E and 9 isolates and 5C isolates, respectively, differed from map I by the absence of one (map type II) or two (map type III) restriction sites. Map type IV, represented by ISG 10A and B (or AG 10) isolates, showed significant restriction site variations, with five enzymes in this region compared with those of the remaining ISGs or AGs. Ten of the 25 restriction sites in the 18S rRNA gene region were informative and selected for analysis. Previously reported restriction maps of the 5.8S rRNA gene region, including the internal transcribed spacers, were aligned with each other, and 12 informative restriction sites were identified. These data were used alone and in combination to evaluate group relationships. Analyses derived from these data sets by maximum parsimony and likelihood methods showed that AG 10 isolates were distinct and distantly related to the majority isolates of the other AGs of this species complex.

Heterokaryon formation with homokaryons derived from protoplasts of Rhizoctonia solani anastomosis group eight

Homokaryons were successfully recovered by regenerating protoplasts prepared from vegetative hyphae of field isolates of Rhizoctonia solani anastomosis group (AG) 8, the causal pathogen of bare-patch disease of cereals. A mating type incompatibility system, which is similar to that reported in AG 1 and AG 4, was demonstrated in AG 8. All homokaryons obtained in AG 8 were able to form tufts with their parent isolates and other heterokaryotic field isolates of AG 8 tested. Heterokaryons were readily recovered from tufts of pairing of certain homokaryon combinations. The synthesized heterokaryons formed tufts with both of the contributing homokaryons. The majority of hyphal tip cultures isolated from tufts resembled one of the contributing homokaryons. These nonheterokaryotic hyphae in tufts are attributed to transient heterokaryon effects.

Role of melanin in susceptibility and resistance of Rhizoctonia solani to microbial lysis

Melanin was detected in self-anastomosing isolates (SAIs) but not in non-self-anastomosing isolates (NSAIs) of anastomosis group (AG) 2-2. Melanin was also detected in isolates of AG 2-1, AG 3 and AG 5, but not of AG 1 and AG 4, The known melanin precursors, catechol and ( + )-scytalone, and inhibitors, Na 2 EDTA, tricyclazole and chlobenthiazone, did not affect hyphal melanization of SAIs and NSAIs. This indicates that the pentaketide or catechol pathway of melanin synthesis may be absent in R. solani . In SAIs, the hyphal cells were composed of extremely thickened walls possessing electron-dense multilayered and microfibrillar structures, whereas in NSAIs the hyphal cell wall was usually very thin, and there was no electron-dense layer even if the cell wall was thick. The hyphal cell wall of AG 1 was also very thin and was transparent. In soil, the longevity of mycelium of SAI was much longer than that of NSAIs. Longevities of isolates of AG 2-1, AG 2-2 and AG 3 were longer than those of AG 1 and AG 4. It seems that there is a correlation between melanin content in the hyphal cell wall and susceptibility or resistance to microbial lysis.

Isolation of a DNA plasmid in the fungus Rhizoctonia solani.

A DNA plasmid, designated pRS64, was detected in three isolates of anastomosis group 4 (AG-4) of Rhizoctonia solani Kühn by biophysical methods. The plasmid was a linear double-stranded DNA with a molecular weight of 1.68 +/- 0.06 X 10(6) or 2617 +/- 87 bp. Weakly pathogenic isolates of R. solani, 1668 RI-1, 1271 RI-64 and 1272 RI-1, which showed abnormally slow growth, contained the plasmids, but pathogenic isolates, 1668, 1271 and 1272, showing normal growth, contained no detectable plasmid DNA.

The Genetics and Pathology of Rhizoctonia Solani

The objective of this paper is to review the genetical and pathological research on Rhizoctonia solani Kuhn from 1965 to the present. In 1965, a symposium, Rhizoctonia solani: Biology and Pathology, was held at Miami, Florida. At this meeting the characteristics of the imperfect stage were defined (60) and the perfect stage accepted as Thanatephorus cucumeris (Frank) Donk (79). It was recognized, however, that T. cucumeris was a collective species and that its nomenclature was not expected to remain stable (79). The past 15 years have been a productive period of research on the pathogen and on the diseases it causes. A number of disease resistant cultivars have been reported and disease control measures have been recom­ mended. The principle most helpful to plant pathologists during this period has been the anastomosis group (AG) concept. This scheme was first suggested in Germany by Schultz in 1937 (74) and later developed by Richter & Schneider in 1953 (66); in Japan by Watanabe & Matsuda in 1966 (82); and in the United States by Parmeter et al in 1969 (59). According to this scheme fusion occurs only between isolates of the same AG. Parmeter et al proposed four AGs (59); Kuninaga et al (49) have expanded the concept to include six AGs and Ogoshi (55) has proposed two subgroups within both AG 1 and AG 2. I will discuss each anastomosis group separately in this paper.