Application of SSR and AFLP to the analysis of genetic diversity in <Emphasis Type="Italic">Gracilariopsis lemaneiformis</Emphasis> (Rhodophyta)

The agarophyte Gracilariopsis lemaneiformis is both important for biological research and of significant economic value. However, the genetic diversity of wild populations of the alga has not been studied. We used amplified fragment length polymorphism (AFLP) PCR and simple sequence repeat (SSR) analysis to investigate diversity in four field populations, three from the coast of Qingdao and one from Weihai, China. Forty G. lemaneiformis isolates collected from the four different geographical groups were analyzed using 16 pairs of SSR primers for PCR amplification. However, no polymorphisms were detected, indicative of a degree of genetic homogeneity. A total of 347 reproducible bands were then amplified using eight AFLP primer pairs, and genetic indices of diversity within and between populations were calculated. This analysis revealed only low levels of genetic diversity both within and between the four geographical groups of G. lemaneiformis. The Weihai population showed a higher within-population genetic diversity than any of the Qingdao populations. The data suggest that there is only limited gene flow between populations. An UPGMA dendrogram revealed two main clusters, and one of these included all the Qingdao isolates. The order of clustering was in accordance with their geographical distribution. These results suggest that the wild G. lemaneiformis populations are closely related and that there is little genetic diversity within wild germplasm in the regions sampled.     

Pathogenic and molecular variation support the presence of genetically distinct clonal lineages in Australian populations of Puccinia graminis f. sp. avenae

Previous studies of the causal agent of stem rust of oats (Puccinia graminis f. sp. avenae; P. g. avenae) in Australia have demonstrated a high level of pathogenic variability. In this work, the pathotypic structure of the Australian P. g. avenae population in 1999 was investigated, as well as the pathotypic and genetic diversity of a collection of 26 Australian isolates representing a 25-year period (1971–1996). In the 1999 sample, 16 races belonging to six international standard races were identified from 97 isolates, with standard race 94 predominant in all regions. Race 94+Pg-13,Pg-Sa,Pg-a, detected in southern New South Wales (sNSW) and northern New South Wales (nNSW), was virulent on all of the differential genotypes used. Detailed analyses of pathogenicity and AFLP variability among 26 isolates collected from 1971–1996 revealed that isolates of standard race 94 collected in 1999 were genetically distinct from other Australian races of P. g. avenae. This evidence, along with data from annual pathogenicity surveys, suggests that the group to which standard race 94 belongs appeared during the late 1980s, and that it increased in frequency to dominate P. g. avenae pathogen populations throughout Australia from 1992 onward. The existence of groups of P. g. avenae isolates in Australia that differ in pathogenicity and AFLP phenotype suggests that current populations have evolved from a number of isolates of the fungus that differ in their genetic backgrounds, which may have originated from independent introductions or from asexual hybridisational events.     

Effect of Yangtze River on population genetic structure of the relict plant Parrotia subaequalis in eastern China

Parrotia subaequalis (Hamamelidaceae) is a Tertiary relic species endemic in eastern China. We used inter‐simple sequence repeat (ISSR) markers to access genetic diversity and population genetic structure in natural five populations of P. subaequalis. The levels of genetic diversity were higher at species level (H = 0.2031) but lower at population level (H = 0.1096). The higher genetic diversity at species levels might be attributed to the accumulation of distinctive genotypes which adapted to the different habitats after Quaternary glaciations. Meanwhile, founder effects on the early stage, and subsequent bottleneck of population regeneration due to its biological characteristics, environmental features, and human activities, seemed to explain the low population levels of genetic diversity. The hierarchical AMOVA revealed high levels (42.60%) of among‐population genetic differentiation, which was in congruence with the high levels of Nei's genetic differentiation index (G_ST = 0.4629) and limited gene flow (N_m = 0.5801) among the studied populations. Mantel test showed a significant isolation‐by‐distance, indicating that geographic isolation has a significant effect on genetic structure in this species. Unweighted pair‐group method with arithmetic average clustering, PCoA, and Bayesian analyses uniformly recovered groups that matched the geographical distribution of this species. In particular, our results suggest that Yangtze River has served as a natural barrier to gene flow between populations occurred on both riversides. Concerning the management of P. subaequalis, the high genetic differentiation among populations indicates that preserving all five natural populations in situ and collecting enough individuals from these populations for ex situ conservation are necessary.     

Genetic Structure and Aggressiveness of Rhizoctonia solani AG1‐IA,the Cause of Sheath Blight of Rice in Southern China

One hundred and eighty isolates of Rhizoctonia solani AG1‐IA, the causal agent of rice sheath blight, were obtained from six locations in southern China. The genetic structure of R. solani isolates was investigated using random amplified polymorphic DNA (RAPD) markers, and a considerable genetic variation among R. solani isolates was observed. Most of the genetic diversity was distributed within populations, rather than among them. The distribution pattern of the genetic variation of R. solani appears to be the result of high gene flow (Nm) and low‐genetic differentiation among populations. The aggressiveness of R. solani was visually assessed by rice seedlings of five different cultivars in the glasshouse. All isolates tested were found to induce significantly different levels of disease severity, reflecting considerable variation in aggressiveness. The isolates were divided into highly virulent, moderately virulent and weakly virulent groups, and the moderately virulent isolates were dominant in R. solani population. No significant correlation was observed among the genetic similarity, pathogenic aggressiveness and geographical origins of the isolates. Information obtained from this study may be useful for breeding for improved resistance to sheath blight.     

基于ISSR的豚草和三裂叶豚草遗传多样性研究

[目的]研究不同地理种群的豚草和三裂叶豚草的遗传多样性水平和遗传结构。[方法]应用筛选的13条ISSR引物对8个豚草居群和7个三裂叶豚草居群共240个样品进行分子标记。[结果]8个豚草居群128个样品,共扩增出304条带,多态性位点比率为98.68%;Shannon''s信息指数为0.6716,Nei''s基因多样性指数为0.4788。7个三裂叶豚草居群112个样品,共扩增出266条带,多态性位点比率为95.86%;Shannon''s信息指数为0.6593,Nei''s基因多样性指数为0.4670。豚草和三裂叶豚草各居群遗传距离较近。[结论]豚草和三裂叶豚草在居群间具有一定的遗传稳定性;居群内具有丰富的遗传多样性。豚草和三裂叶豚草遗传变异主要来源于居群内部。豚草各居群遗传距离和地理距离有显著相关性,三裂叶豚草各居群遗传距离和地理距离无显著相关性。     

Relationships among fourteen species of Satureja growing wild in Iran detected with molecular markers

The genus Satureja is an important plant with a number of aromatic and medicinal properties. In this research, the relative efficiencies of amplified fragment length polymorphism (AFLP) and selectively amplified microsatellite polymorphic loci (SAMPL) were used to detect genetic relationships among 14 species of Satureja, growing wild in Iran. Eleven AFLP and 14 SAMPL primer combinations produced 999 and 1142 scorable bands, respectively, all of the fragments of which were found to be polymorphic. The average genetic similarity values based on Jaccard's coefficient were 0.24 and 0.21 for AFLP and SAMPL, respectively, indicating considerable distance and diversity in the studied germplasm. The correlation coefficients were statistically significant between both marker systems (r = 0.89). UPGMA derived from the combined binary data matrices of both markers depicted genetic distinctions among the studied species and clustered them into two main clusters and several groups. S. edmondi showed the maximum distance from other species and was placed into a single main cluster, while the maximum similarity was obtained between S. rechingeri and S. khuzistanica. Our results indicate that both marker systems are suitable for differentiating individuals and species of this genus.     

Vegetative Compatibility,Pathogenicity and Virulence Diversity of Fusarium oxysporum f. sp. melongenae Recovered from Eggplant

Fusarium oxysporum (Schlechtend.: Fr.) f. sp. melongenae (Fomg) recovered from symptomatic eggplants from five eggplant‐growing areas in Turkey, including the south, west, north‐west, north and south‐east regions. The objective of this study was to investigate the genetic diversity of the Fomg isolates from different geographical location by pathogenicity and VCG tests. Three hundred and seventy‐four Fomg isolates were classified as highly virulent, virulent, moderately virulent and low virulent through pathogenicity assays. No correlation was observed between virulence of Fomg isolates and their locations. The nitrate non‐utilizing mutants (nit) were generated as nit1, nit3 and NitM, based on phenotyping of Fomg growth characteristics of the Fomg isolates on diagnostic media with various sources of nitrogen. The majority of nit mutants (39.4%) recovered were nit1 from minimal medium (MM) containing of 2.0% potassium chlorate (MMC). The most of Fomg isolates were identified as heterokaryon self‐compatible (HSC) based on their ability to form a stable heterokaryon, while four isolates were classified as heterokaryon self‐incompatible (HSI). A large amount of Fomg isolates were vegetatively compatible and assigned as members of the same VCG, whereas nit mutants of 10 Fomg isolates that did not complement with tester strains only paired by themselves (HSC), these isolates were termed vegetative incompatible (vic). The complementation of 33 isolates with tester strains was slow and quite weak, but not paired with themselves even though they are HSC. About 96.3% of the Fomg isolates were assigned to VCG 0320, while the remaining 3.7% were classified as vegetative incompatible group.     

Randomly amplified polymorphic DNA analysis of four different populations of the Indian major carp, Labeo rohita (Hamilton)

The level of genetic variation provides the raw material for selective improvement of a stock. Random amplified polymorphic DNA (RAPD) assay was used to assess the genetic variation in three rivers: the Halda, the Jamuna and the Padma as well as in one hatchery population of the commercially important Indian major carp, Labeo rohita. RAPD markers were amplified from DNA samples of 35 fish from each of the four populations using six decamer random primers. The polymorphic loci proportions were 0.33, 0.28, 0.28 and 0.26 and Nei's gene diversity values were 0.06, 0.07, 0.06 and 0.05 for the Halda, the Jamuna, the Padma and the hatchery populations, respectively. The pairwise population differentiation (F_ST) values indicated a low level of genetic differentiation between the population pairs. From the unweighted pair group method of arithmetic mean (UPGMA) dendrogram based on Nei's genetic distances a correlation between genetic affinities and geographical area was found. The populations were segregated into two groups: the Halda in one group and the Jamuna, the Padma and the hatchery in another group. Overall, the RAPD technique can be introduced as a tool in the population genetics of the rohu fish to provide information on their genetic stock structure.     

Genetic diversity and structure of natural Pinus tabulaeformis populations in North China using amplified fragment length polymorphism (AFLP)

Chinese pine (Pinus tabulaeformis carr.), endemic to China, is a conifer species with extensive and fragmented distribution in North China. In this study, the genetic diversity and structure of 20 natural populations of this species were investigated using amplified fragment length polymorphism (AFLP) markers. A total of 445 fragments were revealed with 8 pairs of primers, 379 (85.17%) of which were polymorphic. A moderate level of genetic diversity was detected at the species level (Shannon's information index I = 0.356, Nei's gene diversity H_E = 0.271) and at the population level (I = 0.219, H_E = 0.206). Most of genetic variation was within populations while a considerable level of genetic differentiation was detected (G_ST = 0.352, Ф_ST = 0.304). The high differentiation could be attributed to the complex and fragmented habitats, and a limited gene flow among populations (N_m = 0.572). The Mantel test indicated that there was significant correlation (r = 0.455, P < 0.001) between Nei's genetic distance and geographical distance among all the populations. The results suggested that proper countermeasures should be taken to prevent the habitat further deterioration and maintain the genetic diversity of this species.     

Pathogenic Variability within Indian Alternaria brassicae Isolates Using Seed,Cotyledon and Leaf of Brassica Species

Thirty Alternaria brassicae (Berk.) Sacc. isolates from diverse geographical locations of India were studied for pathogenic variability on seed, cotyledon and true leaves of Brassica species. Seed germination was reduced maximum by isolate BAB‐39 in Brassica juncea cultivar Varuna (22.1%), Brassica rapa var. Toria cultivar PT‐303 (12%), Brassica carinata cultivar Kiran (12%), Brassica napus cultivar GSL‐1 (11%) and tolerant source of B. juncea genotype PHR‐2 (7%), although least by isolate BAB‐49. Maximum lesion size on leaf was recorded in B. juncea cultivar Rohini (11.2, 16.5 and 16.8 mm) with isolates BAB‐09 (Pantnagar), BAB‐19 (Bharatpur) and BAB‐39 (Kangra), respectively, and categorized as highly virulent, while minimum lesion size of 3.2, 3.7 and 3.8 mm was observed with isolates BAB‐47 (Tonk), BAB 49 (Jobner) and BAB 04 (Kamroop), respectively, considered the weak isolates. On B. alba, BAB‐09, BAB‐19 and BAB‐39 isolates caused maximum lesion size of 3.7, 3.8 and 3.9 mm, respectively, even though it showed maximum tolerance. In both seed and cotyledon inoculation method, the per cent Alternaria blight severity above 80% was observed with isolate of BAB‐39 (91.5%), BAB‐19 (89.0%), BAB‐09 (85.5%) and least in isolate BAB‐49 (34.0%). Brassica seed, cotyledon and leaf showed the similar positive response for categorizing A. brassicae isolates as virulent and avirulent. This information could be used to the development and assessment of resistant brassica germplasm, especially with A. brassicae populations exhibiting increased virulence.     

Assessment of genetic diversity of Iranian Ascochyta rabiei isolates using rep‐PCR markers

Genetic diversity and population structure among 29 isolates of Ascochyta rabiei (AR) obtained from diseased chickpea plants in six different geographical origins in Iran was characterized by MAT and rep‐PCR (BOX/ERIC/REP) markers. Both mating types were found in all six populations, and the frequencies of mating types were variable between populations. The majority of the isolates belonged to Mat1‐1 (58.12%) with the remainder (41.88%) being Mat1‐2. A dendrogram was calculated with Jaccard's similarity coefficients with unweighted pair group method clustering (UPGMA) for the combination of rep‐PCR results, AR strains were differentiated into four clusters (A–D) at 60% similarity level. ERIC, REP and BOX showed a total of 19, 37 and 24 alleles per locus, respectively. Gene diversity (He) and Shannon's information index (I) were the highest in the REP (He = 0.82; I = 2.11), while the lowest values were estimated for the ERIC (He = 0.42; I = 1.3). Our result showed that among the three techniques studied, REP‐PCR produced the most complex amplified banding patterns, which reflected a high degree of diversity among the Iranian AR strains. ERIC‐PCR was the least discriminating method, and BOX‐PCR was intermediate. To the best our knowledge, this is first study of assessment of genetic diversity of AR isolates by rep‐PCR markers.     

Applicability of AFLP Fingerprinting Markers to Molecular Discrimination of the Three Main Fungal Species Associated with Grapevine Decline in Spain

Diplodia seriata, Phaeomoniella chlamydospora and Phaeoacremonium aleophilum are the three main species associated with grapevine decline in Spain. AFLP markers were developed to discriminate Spanish populations of these species. The markers were used to genotype isolates of D. seriata, P. chlamydospora and P. aleophilum. AFLP markers were valuable in performing population genetic studies as genetic variability (K_x) ranged from 0.07 in the P. chlamydospora population to 0.28 in the D. seriata population. Species‐specific markers obtained using only two AFLP combinations clearly discriminate D. seriata, P. chlamydospora and P. aleophilum and are a useful tool in simultaneous identification tests.     

Molecular characterization and genetic diversity analysis of <Emphasis Type="Italic">Jatropha curcas</Emphasis> L. in India using RAPD and AFLP analysis

Jatropha curcas L. belongs to family Euphorbiaceae, native to South America and widely distributed in South and Central America, attained significant importance for its seed oil which can be converted to biodiesel, a renewable energy source alternative to conventional petro-diesel. Very few attempts were made to understand the extent of genetic diversity that exists in J. curcas. Therefore, the present investigation was undertaken to asses the genetic diversity among 28 diverse germplasm collected from distinct geographical areas in India. The overall percentage of polymorphism (PP) was found to be 50.70 and 60.95 by RAPD and AFLP, respectively. The mean PP was found to be 9.72 and 20.57 by RAPD and AFLP, respectively. The mean genetic similarity was observed to be 0.89 by RAPD and 0.88 by AFLP. Among the germplasm JCI20 found to be the most diverged one. The dendrogram analysis of RAPD and AFLP data showed good congruence, but better resolution and more polymorphism was observed with AFLP. When the dendrogram of RAPD was compared with AFLP dendrogram, the major clustering pattern was found to be similar; however, changes in minor grouping were observed. In both RAPD and AFLP analysis clustering of germplasm did not show any correlation with the geographical area of collection. Low genetic diversity observed in J. curcas and the clustering pattern indicates that the distribution of species might have happened through anthropogenic activity and warrants the need for widening the genetic base. The present study will provide pavement for further intra-population studies on narrow geographical areas, to understand the population genetic structure, phylogeography, molecular ecological studies. The marker information and the characterized germplasm help in further improvement of the species through marker assisted breeding programs.     

Genetic diversity of Shiraia bambusicola from East China assessed using ISSR markers

To understand the genetic differentiation of the medicinal fungus Shiraia bambusicola, the genetic diversity of 107 individuals from eight populations collected from Jiangsu, Anhui and Zhejiang provinces were studied using inter-simple sequence repeat (ISSR) analysis. The results revealed that the 11 employed primers produced a total of 241 ISSR loci, of which 240 loci (PPB = 99.6%) were polymorphic. Both Nei's gene diversity indexes and Shannon's gene diversity indexes showed that the genetic differentiation of S. bambusicola primarily occurred within the populations. AMOVA revealed that the variation among populations was 40.0%, and the variation within populations was 60.0%. The results of an unweighted pair group method arithmetic average (UPGMA) analysis and a principal coordinate analysis (PCA) revealed that the populations with minimal geographic separations frequently exhibited regional characteristics. These findings revealed that the relationship between sibship and geographical distribution was intensive.     

New insights into the evolutionary history of Plasmodium falciparum from mitochondrial genome sequence analyses of Indian isolates

Estimating genetic diversity and inferring the evolutionary history of Plasmodium falciparum could be helpful in understanding origin and spread of virulent and drug‐resistant forms of the malaria pathogen and therefore contribute to malaria control programme. Genetic diversity of the whole mitochondrial (mt) genome of P. falciparum sampled across the major distribution ranges had been reported, but no Indian P. falciparum isolate had been analysed so far, even though India is highly endemic to P. falciparum malaria. We have sequenced the whole mt genome of 44 Indian field isolates and utilized published data set of 96 genome sequences to present global genetic diversity and to revisit the evolutionary history of P. falciparum. Indian P. falciparum presents high genetic diversity with several characteristics of ancestral populations and shares many of the genetic features with African and to some extent Papua New Guinean (PNG) isolates. Similar to African isolates, Indian P. falciparum populations have maintained high effective population size and undergone rapid expansion in the past with oldest time to the most recent common ancestor (TMRCA). Interestingly, one of the four single nucleotide polymorphisms (SNPs) that differentiates P. falciparum from P. falciparum‐like isolates (infecting non‐human primates in Africa) was found to be segregating in five Indian P. falciparum isolates. This SNP was in tight linkage with other two novel SNPs that were found exclusively in these five Indian isolates. The results on the mt genome sequence analyses of Indian isolates on the whole add to the current understanding on the evolutionary history of P. falciparum.     

Genetic Relationship of Pyrenophora graminea, P. teres f. maculata and P. teres f. teres Assessed by RAPD Analysis

Barley‐pathogenic Pyrenophora isolates are P. graminea (PG), P. teres f. maculata (PTM) and P. teres f. teres (PTT), which cause foliar leaf stripe, spot blotch and net blotch lesions, respectively. However, the species are often indistinguishable by morphological and cultural characteristics. Random amplified polymorphic DNA (RAPD) analysis has been used to study the genetic relationship amongst 11 PG, 9 PTM and 23 PTT isolates from distant geographical locations. Using seven primers, 55 (52.38%) polymorphic DNA bands were detected out of 105 different fragments amplified in the three pathogens. Genotypic diversity was high as all but two PTT strains had distinct multilocus RAPD fingerprints. Unweighted pair‐group method with arithmetic average (UPGMA) clustering separated the isolates into three main clusters, corresponding to the three pathogens studied. No clear geographical substructuring was found. Nei's gene diversity analysis detected only small differences (max. 6.6%) in band frequencies but considerable levels of differentiation were observed among the pathogen species/forms. However, the variability among the Pyrenophora species/forms (max. 42.0%) was less than within species/forms (max. 58%). Nei's unbiased genetic distance values were in agreement with UPGMA clustering and gene diversity analysis: the two forms of P. teres showed higher divergence from one another (D = 0.132) than the distance found between PG and PTM (D = 0.094). The results suggest that the present taxonomical classification of these morphological taxa may not correspond to their phylogenetic relationship and that there is a very close genetic relationship amongst barley‐pathogenic Pyrenophora species, but genetic exchanges between them could be infrequent.     

Phytophthora infestans Field Isolates from Gansu Province,China are Genetically Highly Diverse and Show a High Frequency of Self Fertility

The genetic diversity of 85 isolates of Phytophthora infestans collected in 2007 from Gansu province in China was determined and compared with 21 isolates collected before 2004. Among them, 70 belonged to the A1 mating type and 15 were self‐fertile (SF). The mitochondrial DNA haplotypes revealed both Ia (25%) and IIa (75%) haplotypes. Metalaxyl resistance occurred with high frequency (54%) in Gansu. Simple sequence repeat (SSR) genotyping revealed 26 genotypes (13 from the Tianshui region) among the 85 isolates, and 18 genotypes among the 21 isolates collected before 2004, without overlap in genotypes detected in the two groups. Cluster analysis showed clear subdivisions within the different mating type isolates. Among Gansu's isolates, Nei's and Shannon's diversity indices were highest in isolates collected in Tianshui where both A1 and SF isolates were found. Analysis of molecular variance of isolates from Gansu indicated that 51% and 49% of the variance was explained by within‐area and among‐area variance, respectively. The results suggest that the occurrence of SF isolates increases the risk of sexual reproduction, the formation of oospore as initial inocula in the field, and affects the genotypic diversity in the population.     

Genetic Diversity of Populations of Monilinia fructicola (Fungi,Ascomycota, Helotiales) from China

ABSTRACT. The genetic variation among 128 isolates of Monilinia fructicola (Fungi, Ascomycota, Helotiales) from China was analyzed using Inter‐Simple Sequence Repeat (ISSR) markers and compared with those of samples from California, USA and New Zealand. A total of 72 reproducible DNA fragments were scored, of which 87.5% (63/72) were polymorphic. The Nei's gene diversity and Shannon's diversity indices of three Chinese regional populations were very similar to that from California. However, several differences were observed among geographic populations of M. fructicola from both within China and between China and California. The analysis of molecular variance (AMOVA) of isolates from different geographic locations suggested that most of the observed genetic variation was found within populations. Results of this study are inconsistent with the hypothesis that the Chinese populations of M. fructicola were derived from a single or few recent migrants from other countries. Instead, our results suggest that M. fructicola has been in China long before its first official recording in 2003.     

Genetic diversity of natural populations of Larix principis-rupprechtii in Shanxi Province,China

Prince Rupprecht's Larch (Larix principis-rupprechtii Mayr.) is one of dominant components of middle and high elevation forests in North China. Shanxi Province is well known as “the Hometown of Prince Rupprecht's Larch” in China. In this study, six natural populations of this species across Shanxi were selected to investigate the genetic variation of the species using amplified fragment length polymorphism (AFLP) markers. Results showed that in comparison with some other species of Larix, higher genetic diversity was revealed at the species level for L. principis-rupprechtii (percentage of polymorphic loci PPL = 71.9%, Nei's gene diversity H_E = 0.225, Shannon information index I = 0.341). Most of genetic variation existed within populations (80.5%), while the genetic differentiation among populations was significant (p < 0.001) and higher (G_st = 0.194) than most other species of Larix. The differentiation can be attributed to the limited gene flow (N_m = 1.035) among populations, which could be due to the spatial isolation and habitat fragmentation. The six populations can be divided into three groups based on the Nei's genetic distances between populations (from 0.033 to 0.076). There was no significant correlation (r = 0.268, p > 0.05) between genetic distance and geographic distance among populations. The measures for in-situ or ex-situ conservation should be taken to preserve the genetic diversity of this species.     

Population Structure and Development of Resistance to Hymexazol Among Fusarium solani Populations from Date Palm,Citrus and Cucumber

A study was conducted to investigate genetic diversity and sensitivity to hymexazol among 80 isolates of Fusarium solani complex obtained from date palm (30), citrus (31) and cucumber (19). Characterization based on sequences of the EF1α and ITS rRNA showed that isolates belong to F. solani complex MLST type 3 + 4. AFLP analysis produced 980 polymorphic loci, 80 AFLP genotypes and moderate levels of genetic diversity (H = 0.2494). Clustering of the isolates was not related to the host or the geographical origin of the isolates. Analysis of molecular variance (amova ) indicated the existence of a low level of genetic differentiation among populations obtained from different hosts (F_st = 0.0162) and regions (F_st = 0.0066). This may provide evidence for frequent movement of inoculum among hosts and regions in Oman, which could be attributed to cultural practices employed by farmers. Isolates of F. solani displayed variation in sensitivity to hymexazol, with EC₅₀ values ranging from 2 to 5745 μg/ml (mean = 878 μg/ml); 19% of the isolates have an EC₅₀ value of more than 1000 μg/ml. Findings are discussed in terms of the factors that affect diversity in F. solani isolates. The study reports for the first time the development of resistance to hymexazol among F. solani isolates from date palm, citrus and cucumber.