Rulin Zhan

First Report of Fusarium mangiferae Causing Mango Malformation in China

Mango (Mangifera indica L.) malformation caused by Fusarium mangiferae has been reported in many mango-growing regions of the world (3). The disease was also observed in Yunnan and Sichuan provinces of China (1). Typical symptoms in seedlings included loss of apical dominance, hyperplasia and hypertrophy of vegetative buds, shortened internodes, and leaves that were more brittle than those of healthy plants. Inflorescences were abnormally branched and thickened, with panicles producing as much as two to five times the normal number of flowers. Flowers in the malformed inflorescence were much more enlarged and crowded than the generally hypertrophied axes of the panicle, thus producing no fruit or aborting early. To identify the pathogen, samples of malformed and healthy mango seedlings were collected from the affected plantings. For isolation, portions of stems were cut into 3- to 4-mm segments, surface disinfested, dried, and then plated on potato dextrose agar and incubated at 25°C. Within 5 days, white, fluffy, aerial mycelium developed. With the aid of an inverted microscope, single conidia were transferred to carnation leaf agar (CLA) medium. After 10 days of incubation, morphological characteristics were found to be identical to those of F. mangiferae (4). Aerial mycelium was white with no pigmentation observed on potato sucrose agar. Pigmentation on rice medium was pink. On CLA medium, conidia grew in branched conidiophores with false heads bearing monophialides or polyphialides. No conidiospores in chains were observed. Microconidia were ovate to long and oval, 0 to 1 septate, and 3.1 to 10.2 × 1.5 to 2.2 μm. Macroconidia are falculate, 3 to 5 septate, and 18 to 38 × 1.8 to 2.4 μm. Chlamydospores were not observed. Pathogenicity studies were conducted with 7-month-old asymptomatic mango seedlings. These seedlings, except for the controls, were inoculated by injection of the isolated fungus in the axillary or apical bud position. A 1-ml spore suspension (1 × 106 spores/ml) was injected slowly into the stems using a microsyringe with three buds per seedling, for a total of 10 seedlings. Typical malformation symptoms developed within 3 to 4 months, and none of the plants inoculated with sterile water resulted in malformation symptoms. Reisolations from the induced malformed shoots yielded the same fungus, and no fungal growth was observed to be growing from the control plants. To confirm identity of the causal fungus, the gene encoding translation elongation factor 1 alpha (EF-1α) was amplified and sequenced (2). The EF-1α sequence was 660 bp long. The sequence (GenBank Accession No. HM068871) was 99.68% similar to sequences of FD_01167 in the Fusarium ID database. On the basis of symptoms, fungal morphology, the EF-1α region sequence, and pathogenicity testing, this fungus was identified as F. mangiferae. To our knowledge, this is the first report of F. mangiferae causing mango malformation in China. This report will establish a foundation for further study of F. mangiferae and effectively addressing the disease. References: (1) X. H. Chen. Pract. Technol. (in Chinese) 6:5, 1992. (2) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (3) J. Kumar et al. Annu. Rev. Phytopathol. 31:217, 1993. (4) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006.

Transcription Profiling Analysis of Mango–Fusarium mangiferae Interaction

Malformation caused by Fusarium mangiferae is one of the most destructive mango diseases affecting the canopy and floral development, leading to dramatic reduction in fruit yield. To further understand the mechanism of interaction between mango and F. mangiferae, we monitored the transcriptome profiles of buds from susceptible mango plants, which were challenged with F. mangiferae. More than 99 million reads were deduced by RNA-sequencing and were assembled into 121,267 unigenes. Based on the sequence similarity searches, 61,706 unigenes were identified, of which 21,273 and 50,410 were assigned to gene ontology categories and clusters of orthologous groups, respectively, and 33,243 were mapped to 119 KEGG pathways. The differentially expressed genes of mango were detected, having 15,830, 26,061, and 20,146 DEGs respectively, after infection for 45, 75, and 120 days. The analysis of the comparative transcriptome suggests that basic defense mechanisms play important roles in disease resistance. The data also show the transcriptional responses of interactions between mango and the pathogen and more drastic changes in the host transcriptome in response to the pathogen. These results could be used to develop new methods to broaden the resistance of mango to malformation, including the over-expression of key mango genes.

The occurrence of two species of pineapple mealybugs (Dysmicoccus spp.) (Hemiptera: Pseudococcidae) in China and their genetic relationship based on rDNA ITS sequences

To explore the composition, distribution and interrelation of the pineapple mealybugs in China, samples were collec from 14 counties of five provinces. The genetic variations of pineapple mealybugs from China, Brazil and Hawaii of USA have been analyzed. The whole ribosomal internal transcribed spacer 1 (ITS1), 5.8S and ribosomal internal transcribed spacer 2 (ITS2) were sequenced for all samples. Pink pineapple mealybug (PPM), Dysmicoccus brevipes (Cockerell) and gray pineapple mealybug (GPM), Dysmicoccus neobrevipes Beardsley are found causing damage on Ananas comosus (L.) Merr. PPM is a predominant species of mealybug on A. comosus in China. Though GPM has wider host range in China, PPM has larger distribution area than GPM. The results showed that two pineapple mealybug species belong to two different clades based on the sequences of ITS. PPM from China was found to have four haplotypes, and GPM had two haplotypes. The genetic variation of PPM is greater than that of GPM, though both of them had one predominant haplotype. One haplotype of PPM was found in samples from mainland China, and three from Hainan Island. Another haplotype of PPM was observed among the samples from Brazil and Hawaii. However, mealybugs from Wanning City of Hainan Island in China represented a different lineage that clearly diverged from other populations, which would be of a cryptic lineage or species in the pink pineapple mealybug complex. Mealybugs from Wanning City are probably native and were present long before the exotic pink pineapple mealybug was introduced in the early twentieth century. Most GPM, represented by a predominant haplotype, was widely found on sisal in plantations in south China. Other GPM, often found on sisal in urban green belt in south China, was of different haplotype from samples on sisal in plantations, probably originating from Taiwan.