Colletotrichum species are plant pathogens, saprobes, and endophytes on a range of economically important hosts. However, the species occurring on pear remain largely unresolved. To determine the morphology, phylogeny and biology of Colletotrichum species associated with Pyrus plants, a total of 295 samples were collected from cultivated pear species (including P. pyrifolia, P. bretschneideri, and P. communis) from seven major pear-cultivation provinces in China. The pear leaves and fruits affected by anthracnose were sampled and subjected to fungus isolation, resulting in a total of 488 Colletotrichum isolates. Phylogenetic analyses based on six loci (ACT, TUB2, CAL, CHS-1, GAPDH, and ITS) coupled with morphology of 90 representative isolates revealed that they belong to 10 known Colletotrichum species, including C. aenigma, C. citricola, C. conoides, C. fioriniae, C. fructicola, C. gloeosporioides, C. karstii, C. plurivorum, C. siamense, C. wuxiense, and two novel species, described here as C. jinshuiense and C. pyrifoliae. Of these, C. fructicola was the most dominant, occurring on P. pyrifolia and P. bretschneideri in all surveyed provinces except in Shandong, where C. siamense was dominant. In contrast, only C. siamense and C. fioriniae were isolated from P. communis, with the former being dominant. In order to prove Koch's postulates, pathogenicity tests on pear leaves and fruits revealed a broad diversity in pathogenicity and aggressiveness among the species and isolates, of which C. citricola, C. jinshuiense, C. pyrifoliae, and C. conoides appeared to be organ-specific on either leaves or fruits. This study also represents the first reports of C. citricola, C. conoides, C. karstii, C. plurivorum, C. siamense, and C. wuxiense causing anthracnose on pear.

Species of Diaporthe (syn. Phomopsis) are important endophytes, saprobes and pathogens, infecting a wide range of plants and resulting in important crop diseases. However, the species occurring on pear remain largely unresolved. In this study, a total of 453 Diaporthe isolates were obtained from branches of Pyrus plants (including P. bretschneideri, P. communis, P. pyrifolia and P. ussuriensis collected from 12 provinces in China) showing shoot canker symptoms. Phylogenetic analyses based on five loci (ITS, TEF, CAL, HIS, and TUB) coupled with morphology of 113 representative isolates revealed that 19 Diaporthe species were isolated, representing 13 known species (including D. caryae, D. cercidis, D. citrichinensis, D. eres, D. fusicola, D. ganjae, D. hongkongensis, D. padina, D. pescicola, D. sojae, D. taoicola, D. unshiuensis and D. velutina) and six new species described here as D. acuta, D. chongqingensis, D. fulvicolor, D. parvae, D. spinosa and D. zaobaisu. Although Koch's postulates confirmed all species to be pathogenic, a high degree of variation in aggressiveness was observed. Moreover, these species have a high diversity, plasticity, and prevalence related to the geographical location and pear species involved.

In recent years, a widespread canker disease that infects the branches of pear trees has been observed in many provinces in China; it kills the branches and results in high losses in fruit production. Symptomatic branches were collected for etiological isolation from 11 varieties of three pear species and from Malus pumila. Samples were collected from six provinces in China. In total, 143 Phomopsis isolates were obtained from 181 samples and these were identified as belonging to five species: Phomopsis fukushii (n = 69 isolates), Diaporthe eres (n = 31), P. amygdali (n = 22), P. longicolla (n = 13), and D. neotheicola (n = 8). Pathogenicity tests showed that only the first three species induced lesions on nonwounded branches of Pyrus pyrifolia var. Cuiguan. All the fungal species induced branch cankers following wound inoculations, and tests with additional pear varieties showed significantly higher virulence levels for the first three species than the latter two. A host range evaluation suggested that the five species could infect most fruit trees belonging to the Rosaceae family as well as some non-Rosaceous species. Virulence varied depending on the species of both host and pathogen. Isolates of Phomopsis amygdali had significantly higher virulence in all the tested Rosaceae plants. Correlations among the host, pathogen, and sampling regions were noted, and the morphology, growth rate, and sporulation of these species in varied media were also characterized. This study presents the first attempt to perform a broad survey and characterization of the Phomopsis spp. associated with the pear shoot cankers in China. This study shows that D. eres and P. amygdali are just as responsible for the pear shoot canker diseases as P. fukushii, and it expands the host and geographic ranges of the five species. This report provides useful information for understanding and improving management strategies for controlling this economically important disease.

Puccinia striiformis f. sp. tritici (Pst) causes wheat stripe rust (also called yellow rust, Yr), one of the most important diseases worldwide. Characterization of virulence in Pst populations is essential for developing wheat cultivars with effective and durable resistance to control the disease. A total of 138 Pst races, including 120 races that were not previously reported, were identified from stripe rust collections made from Canada, China, Ecuador, Egypt, Italy and Mexico in 2013–2020 using a set of 18 Yr single-gene differentials. Virulence of the resistance gene Yr5 or Yr15 was not found in isolates from any of the countries, indicating their effectiveness against the Pst populations. Virulence to 16 Yr genes was detected, but the frequencies varied greatly among countries. On average, the frequencies of virulence to Yr6, Yr7, Yr9, Yr43, Yr44 and YrExp2 were high (81.7–90.6%), those to Yr1, Yr8, Yr17, Yr27, YrSP and Yr76 were moderate (34.0–56.8%), and those to Yr10, Yr24, Yr32 and YrTr1 were low or very low (0.4–18.5%). The same races detected in different countries and different races from different countries clustered into the same virulence groups, indicating Pst migration among different countries, especially between eastern Asia and the Mediterranean region. These results should be useful for breeding wheat cultivars with effective resistance to stripe rust in these countries as well as globally.

Puccinia striiformis f. sp. tritici causes stripe rust (yellow rust), one of the most important wheat diseases worldwide. To understand the genetic variation of the pathogen in a global scale, 283 P. striiformis f. sp. tritici isolates collected from 16 countries in eight geographic regions were genotyped using 24 codominant simple sequence repeat markers. The overall collection had a high level of genetic diversity, and the diversity levels in the Asian populations were generally higher than those of the other regions. Heterozygosity of isolates ranged from 0 to 75%, with an average of 46%. Mean heterozygosity in individual countries ranged from 34 to 59%. A total of 265 multilocus genotypes (MLGs) were detected, which were classified into eight molecular groups. Some of the molecular groups were present in all geographic regions. Moreover, many isolates from different regions were found to be identical or very closely related MLGs. Analysis of molecular variance revealed high variation within countries and intermediate variation between countries, but it revealed low and insignificant variation among geographic regions. Pairwise comparisons of regional populations detected considerable effective migrants and only low to moderate levels of differentiation. The molecular genotypes had a moderate level of correlation with the virulence phenotypes, and some of the molecular/virulence groups contained isolates from different continents. The results indicate tremendous migrations of P. striiformis f. sp. tritici and warrant the development of management strategies considering the global pathogen population.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat worldwide. To understand the worldwide distribution of its molecular groups, as well as the diversity, differentiation, and migration of the Pst populations, 567 isolates collected from nine countries (China, Pakistan, Italy, Egypt, Ethiopia, Canada, Mexico, Ecuador, and the U.S.) in 2010–2018 were genotyped using 14 codominant simple sequence repeat markers. A total of 433, including 333 new multi-locus genotypes (MLGs), were identified, which were clustered into ten molecular groups (MGs). The MGs and country-wise populations differed in genetic diversity, heterozygosity, and correlation coefficient between the marker and virulence data. Many isolates from different countries, especially the isolates from Mexico, Ecuador, and the U.S., were found to be identical or closely related MLGs, and some of the MGs were present in all countries, indicating Pst migrations among different countries. The analysis of molecular variance revealed 78% variation among isolates, 12% variation among countries, and 10% variation within countries. Only low levels of differentiation were found by the pairwise comparisons of country populations. Of the 10 MGs, 5 were found to be involved in sexual and/or somatic recombination. Identical and closely related MLGs identified from different countries indicated international migrations. The study provides information on the distributions of various Pst genetic groups in different countries and evidence for the global migrations, which should be useful in understanding the pathogen evolution and in stressing the need for continual monitoring of the disease and pathogen populations at the global scale.