First Report of Colletotrichum karstii Causing Anthracnose on Blueberry Leaves in Brazil

What's in my Pot? Six Colletotrichum Species Causing Anthracnose in Brazilian Pecan Orchards

Pecan (Carya illinoinensis) is one important exotic forest crop cultivated in South America, specifically in Brazil, Uruguay, and Argentina. However, diseases such as anthracnose, favored by high humidity conditions and high summer temperatures, make its cultivation difficult, causing important loss to pecan farmers. This study used morphological and molecular approaches to identify the Colletotrichum species causing anthracnose in pecan plantations in Southern Brazil. The isolates obtained from pecan fruits with anthracnose symptoms were grouped through quantitative morphological characteristics into three distinct morphotypes. Molecular analysis of nuclear genes allowed the identification of six species of Colletotrichum causing anthracnose in pecan: C. nymphaeae, C. fioriniae, C. gloeosporioides, C. siamense, C. kahawae, and C. karsti. Three of these species are reported for the first time as causal agents of anthracnose in pecan. Therefore, these results provide an important basis for the adoption and/or development of anthracnose management strategies in pecan orchards cultivated in southern Brazil and neighboring countries.

Colletotrichum Species Associated with Peaches in China

Colletotrichum is regarded as one of the 10 most important genera of plant pathogens in the world. It causes diseases in a wide range of economically important plants, including peaches. China is the largest producer of peaches in the world but little is known about the Colletotrichum spp. affecting the crop. In 2017 and 2018, a total of 286 Colletotrichum isolates were isolated from symptomatic fruit and leaves in 11 peach production provinces of China. Based on multilocus phylogenetic analyses (ITS, ACT, CAL, CHS-1, GAPDH, TUB2, and HIS3) and morphological characterization, the isolates were identified to be C. nymphaeae, C. fioriniae, and C. godetiae of the C. acutatum species complex, C. fructicola and C. siamense of the C. gloeosporioides species complex, C. karsti of the C. boninense species complex, and one newly identified species, C. folicola sp. nov. This study is the first report of C. karsti and C. godetiae in peaches, and the first report of C. nymphaeae, C. fioriniae, C. fructicola, and C. siamense in peaches in China. C. nymphaeae is the most prevalent species of Colletotrichum in peaches in China, which may be the result of fungicide selection. Pathogenicity tests revealed that all species found in this study were pathogenic on both the leaves and fruit of peaches, except for C. folicola, which only infected the leaves. The present study substantially improves our understanding of the causal agents of anthracnose on peaches in China.

First Report of Colletotrichum chrysophilum Causing Anthracnose on Blueberry in Brazil

Highbush (Vaccinium corymbosum L.) and rabbiteye (V. ashei R.) blueberry are the most important export small fruit crops in southern Brazil. Anthracnose has been considered one of the most destructive disease and exclusively associated with C. karstii in Brazil (Rios et al. 2014). In November 2019, severe anthracnose symptoms including leaf spots but particularly twig blights and fruit rots were observed on all blueberry plants (V. ashei) in one organic orchard in Santa Catarina state, Brazil (27º43'48.96"S, 49º0'57.79"W). Four isolates were obtained from necrotic lesions and monosporic cultures were grown on potato dextrose agar at 25°C and with a 12 h photoperiod under near ultra violet light. After 15 days, colonies showed upper surface color varying from grayish-white to pale-orange and the reverse side pale-orange. Conidia were hyaline, cylindrical with rounded ends, and their length and width ranged from 9.5 to 15.5 µm (x ̅=11.8) and 6.5 to 3.5 µm (x ̅=4.9), respectively. The isolates were identified by multilocus phylogenetic analyses using nucleotide sequences of actin (ACT), β-tubulin (TUB2), calmodulin (CAL), glyceraldehyde-3-phosphate-dehydrogenase (GAPDH), glutamine synthetase (GS), internal transcribed spacer (ITS) and the intergenic spacer between DNA lyase and the mating-type locus MAT1-2-1 (ApMAT). Nucleotide sequences exhibited from 95 to 100% sequence identity to Colletotrichum chrysophilum ex-type (CMM4268) and were deposited in GenBank database (MW868219 to MW868222, MW868211 to MW868214, MW868215 to MW868218, MW868223 to MW868226, MW868202 to MW868205, MW793353 to MW793356, and MW868207 to MW868210). C. chrysophilum belongs to the C. gloeosporioides species complex and was previously described as C. ignotum in banana and other tropical fruits in Brazil (Vieira et al. 2017; Veloso et al. 2018). In addition, this species was recently reported on apple fruit in New York, USA (Khodadadi et al. 2020). To confirm pathogenicity, one-year-old blueberry plants were inoculated by spraying a suspension of 1×106 conidia/ml, incubated in a moist chamber in the dark for 48 h and then kept in the greenhouse. Plants sprayed with sterile distilled water served as control. Additionally, fruits were immersed for 2 min in a conidial suspension (1×106 conidia/ml) and incubated at 25°C and 12 h photoperiod for 20 days. Inoculated plants exhibited first symptoms in twigs at 10 days after inoculation (dai). Infected twigs showed initially dark brown spots that coalesced and became necrotic. On leaves, reddish-brown lesions with less than 2 mm appeared at low intensity at 15 dai. On fruits, sunken areas associated with an abundant orange mucilaginous mass of acervuli and conidia were seen at 7 dai. Symptoms on plants were identical to those observed under field conditions, and the pathogen was re-isolated from lesions fulfilling Koch's postulates. To the best knowledge, this is the first report of C. chrysophilum causing anthracnose on blueberries in Brazil. The identification of this species causing blueberry anthracnose is crucial to improve the disease control strategies and resistance breeding.

Identification of Colletotrichum Species Associated with Blueberry Anthracnose in Sichuan, China

Anthracnose caused by Colletotrichum spp. is an important disease of blueberries and results in large economic losses for blueberry growers. Samples of anthracnose were collected from six main blueberry cultivation areas in Sichuan Province. In total, 74 Colletotrichum isolates were obtained through a single-spore purification method and identified to the species through morphological characteristics and phylogenetic analyses based on partial DNA sequences of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), internal transcribed spacer (ITS) regions, and the β-tubulin (TUB2), actin (ACT) and calmodulin (CAL) genes. Among all species, Colletotrichum fructicola was the most dominant species, with an isolation percentage of up to 66.2% in Sichuan, followed by Colletotrichum siamense (17.6%), C. kahawae (5.4%), C. karstii (5.4%), C. nymphaeae (2.7%) and C. sichuaninese (2.7%). Pathogenicity tests showed all species were able to cause typical anthracnose symptoms on blueberry leaves and stems. Colletotrichum fructicola was the predominant species with strong aggressiveness. Moreover, C. fructicola, C. kahawae, C. sichuaninese and C. nymphaeae are first reported here to cause blueberry anthracnose. This study provides a comprehensive reference for the association of different Colletotrichum spp., which may support the sustainable management of blueberry anthracnose.