Weeds Harbor Fusarium Species that Cause Malformation Disease of Economically Important Trees in Western Mexico.

Mango malformation disease (MMD) caused by Fusarium spp. is an important limiting factor in most production areas worldwide. Fusarium mexicanum and F. pseudocircinatum have been reported as causing MMD in Mexico. These two pathogens also cause a similar disease in Swietenia macrophylla (big-leaf mahogany malformation disease) in central western Mexico, and F. pseudocircinatum was recently reported as causing malformation disease in Tabebuia rosea (rosy trumpet) in the same region. These studies suggest that additional plant species, including weeds, might be hosts of these pathogens. The role that weed hosts might have in the disease cycle is unknown. The objectives of this work were to recover Fusarium isolates from understory vegetation in mango orchards with MMD, identify the Fusarium isolates through DNA sequence data, and determine whether F. mexicanum is capable of inducing disease in the weedy legume Senna uniflora (oneleaf senna). Additional objectives in this work were to compare Fusarium isolates recovered from weeds and mango trees in the same orchards by characterizing their phylogenetic relationships, assessing in vitro production of mycotoxins, and identifying their mating type idiomorph. A total of 59 Fusarium isolates from five species complexes were recovered from apical and lateral buds from four weed species. Two of the species within the F. fujikuroi species complex are known to cause MMD in Mexico. Trichothecene production was detected in five isolates, including F. sulawense and F. irregulare in the F. incarnatum-equiseti species complex and F. boothii in the F. sambucinum species complex. Both mating types were present among mango and weed isolates. This is the first report of herbaceous hosts harboring Fusarium species that cause mango malformation in Mexico. The information provided should prove valuable for further study of the epidemiological role of weeds in MMD and help manage the disease.

Malformation Disease in Tabebuia rosea (Rosy Trumpet) Caused by Fusarium pseudocircinatum in Mexico.

Tabebuia rosea (rosy trumpet) is an economically important neotropical tree in Mexico that is highly valued for the quality of its wood, which is used for furniture, crafts, and packing, and for its use as an ornamental and shade tree in parks and gardens. During surveys conducted in the lower Balsas River Basin region in the states of Guerrero and Michoacán, symptoms of floral malformation were detected in T. rosea trees. The main objectives of this study were to describe this new disease, to determine its causal agent, and to identify it using DNA sequence data. A second set of objectives was to analyze the phylogenetic relationship of the causal agent to Fusarium spp. associated with Swietenia macrophylla trees with malformation surveyed in the same region and to compare mycotoxin production and the mating type idiomorphs of fusaria recovered from T. rosea and S. macrophylla. Tabebuia rosea showed malformed inflorescences with multiple tightly curled shoots and shortened internodes. A total of 31 Fusarium isolates recovered from symptomatic T. rosea (n = 20) and S. macrophylla (n = 11) trees were identified by molecular analysis as Fusarium pseudocircinatum. Pathogenicity tests showed that isolates of F. pseudocircinatum recovered from T. rosea induced malformation in inoculated T. rosea seedlings. Eighteen F. pseudocircinatum isolates were tested for their ability to produce mycotoxins and other secondary metabolites. Moniliformin, fusaric acid, bikaverin, beauvericin, aurofusarin. and 8-O-methylbostrycoidin were produced by at least one strain of the 18 isolates tested. A multiplex PCR assay for mating type idiomorph revealed that 22 F. pseudocircinatum isolates were MAT1-1 and that 9 were MAT1-2. Here, we report a new disease of T. rosea in Mexico caused by F. pseudocircinatum.

Genetic diversity of Fusarium pseudocircinatum in the central western region of Mexico: the case of big-leaf mahogany malformation disease.

Fusarium pseudocircinatum is the main causal agent of big-leaf mahogany malformation disease (BLMMD) of mahogany (Swietenia macrophylla) in Mexico. Although, BLMMD is the most important disease for this high-value timber species, there is a lack of information on the genetic variation present in geographically diverse isolates of F. pseudocircinatum. The objective of this study was to determine the genetic diversity of populations of F. pseudocircinatum causing BLMMD in the central western region of Mexico. A total of 611 big-leaf mahogany trees were inspected at eight sites in four states (Colima, Guerrero, Jalisco and Michoacán); of these, 42.7% showed malformation symptoms similar to those of BLMMD. Of 374 Fusarium isolates that were recovered, 277 were identified as F. pseudocircinatum, 56 were F. mexicanum, and 41 were Fusarium spp. An ISSR analysis of the F. pseudocircinatum isolates generated 51 bands of which 38 were polymorphic (76.8%) with a mean of 17 bands per primer. A total of 87 multilocus genotypes (MLGs) were identified. Nei's genetic diversity analysis showed that the isolates had a high genetic diversity average (0.147), with values ranging from 0.070 to 0.365 depending of the geographical location. An analysis of molecular variance revealed that the variation within the populations was low (27.36%), while the variation within MLGs was significant (72.64%), indicating genetic flow. Overall, the genetic variability of F. pseudocircinatum populations was high and the MLGs from Colima (Colima) and Gabriel Zamora (Michoacán) were placed centrally, which possibly is evidence of ancestry and indicates its dispersion routes in the central western region of Mexico.

Genetic diversity of Fusarium mexicanum, causal agent of mango and big-leaf mahogany malformation in Mexico.

In Mexico, Fusarium mexicanum has been reported causing mango malformation disease and big-leaf mahogany malformation disease. Our objective was to determine the genetic diversity of F. mexicanum isolates obtained from malformed big-leaf mahogany and mango trees, using an internal simple sequence repeat (ISSR) analysis. A total of 61 isolates of F. mexicanum, 32 from mango and 29 from big-leaf mahogany, were initially genotyped using fourteen ISSR primers. Data from five primers that produced the highest number of polymorphic bands were selected for further analysis. The primers generated 49 polymorphic bands (85.96%) from a total of 57 fragments ranging in size from 250 to 2800 bp, with an average of 11.4 bands per primer. An analysis of molecular variance (AMOVA) indicated that the variation within populations, isolates grouped by host and geographic origin, was significant (43%), followed by the variation between the big-leaf mahogany versus mango isolates (34%), while among populations the variation was the lowest (22%). The genetic fingerprints suggested that genetic variability of F. mexicanum populations are structured by the host of origin rather than the geographic region.