Resistance in Mango Against Infection by Ceratocystis fimbriata

This study was designed to characterize and describe host cell responses of stem tissue to mango wilt disease caused by the fungus Ceratocystis fimbriata in Brazil. Disease progress was followed, through time, in inoculated stems for two cultivars, ‘Ubá’ (field resistant) and ‘Haden’ (field susceptible). Stem sections from inoculated areas were examined using fluorescence light microscopy and transmission and scanning electron microscopy, coupled with energy-dispersive X-ray microanalysis. Tissues from Ubá colonized by C. fimbriata had stronger autofluorescence than those from Haden. The X-ray microanalysis revealed that the tissues of Ubá had higher levels of insoluble sulfur and calcium than those of Haden. Scanning electron microscopy revealed that fungal hyphae, chlamydospores (aleurioconidia), and perithecia-like structures of C. fimbriata were more abundant in Haden relative to Ubá. At the ultrastructural level, pathogen hyphae had grown into the degraded walls of parenchyma, fiber cells, and xylem vessels in the tissue of Haden. However, in Ubá, plant cell walls were rarely degraded and hyphae were often surrounded by dense, amorphous granular materials and hyphae appeared to have died. Taken together, the results of this study characterize the susceptible and resistant basal cell responses of mango stem tissue to infection by C. fimbriata.

First Report on the Association Between Ceratocystis fimbriata, an Agent of Mango Wilt, Xyleborus affinis, and the Sawdust Produced During Beetle Colonization in Brazil

Mango (Mangifera indica L.) is an economically important fruit crop in many tropical and subtropical regions. Recently, the wilt disease caused by Ceratocystis fimbriata has limited mango production in Brazil and other countries (3). There are reports that Hypocryphalus mangifera (Coleoptera: Curculionidae) is a vector of Ceratocystis spp. and that other beetles, such as Xyleborus affinis (Coleoptera: Curculionidae), may attack mango trees and excavate gallery burrows, thereby producing sawdust (1,3). In March 2011, X. affinis was found colonizing diseased mango trees located in Itaperuna, Rio de Janeiro State (21°12′23″ S, 41°53′23″ W). Therefore, we aimed to evaluate whether both the beetle and the sawdust produced in colonized trees would be associated with C. fimbriata. In March 2011, three isolates of C. fimbriata were collected: CF01 in sawdust from ‘Espada’ trees with wilt symptoms (yellowish to dried leaves, dried stems, and gum exudation from the stem) in Itaperuna; CF02 from X. affinis colonizing wilted trees in Itaperuna; and CF03 from wilted ‘Palmer’ trees in Frutal, Minas Gerais State (20°1′11″ S, 48°55′10″ W). To obtain the isolates, fragments of sawdust, beetles, and mango stem were set between carrot disks and incubated in a wet chamber at 25°C with 12 h of light (4). After 10 days, the ascospores produced in perithecia in the carrot tissue were directly transferred to potato dextrose agar (PDA) in 9-cm petri dishes and incubated at 25°C with 12 h of light. After 10 days, 1-cm mycelial disks were taken from the borders of actively growing colonies. In each of 20 seedlings of 8-month-old ‘Espada,’ growing in 18 × 25 cm plastic pots with a soil-sand-cow manure mixture (3:1:1, v/v), a 1-cm diameter wound in the stem was made with a cork borer (20 cm above the soil surface). A mycelial disk was placed in each wound (a plain PDA disk was placed in control plants). After inoculation, a wet cotton plug was placed on the wound, which was then wrapped with Parafilm. Five plants were inoculated in each treatment. The seedlings were checked weekly for up to 56 days after inoculation. All three isolates were pathogenic, causing typical disease symptoms on the plants, beginning 7 days after inoculation: gum exudation (60, 60, and 0%); and yellowish and wilt (80, 100, and 80%). The % values are for isolates CF01, CF02, and CF03, respectively. No disease symptoms were observed in the control seedlings. After reisolating, the three isolates were confirmed as being C. fimbriata: perithecia (110 to 250 μm wide, 120 to 250 μm tall), base dark, globose, and long dark necks (440 to 770 μm long, 28 to 40 μm wide); ascospores hyaline, one-celled, galeate (5.0 to 7.5 μm long, 3.5 to 5.0 μm wide), exuded in sticky and cream colored mass at the apex of the perithecium neck (2). To our knowledge, this is the first report of an association between C. fimbriata and both X. affinis and the sawdust produced during beetle colonization. Therefore, both the beetle and the sawdust are potential dispersal agents of C. fimbriata in mango orchards. This finding is epidemiologically important, and the disease spread related to both sawdust and beetle is being followed in the field. References: (1) A. O. Al Adawi et al. Eur. J. Plant. Pathol. 135:243, 2013. (2) C. J. B. Engelbrecht and T. C. Harrington. Mycologia 97:57, 2005. (3) A. Masood et al. Pakistan J. Zool. 44:1545, 2012. (4) W. J. Moller and J. E. De Vay. Phytopathology 58:123, 1968.