South American leaf blight of Hevea brasiliensis: spore dispersal of Microcyclus ulei

Abstract

Trapping of ascospores and conidia of Microcyclus ulei among young trees of Hevea brasiliensis in Trinidad from May 1973 to May 1975 showed that ascospores occurred throughout the year whilst conidia were present only during the wet season. Peak ascospore concentrations occurred in August and November during the wet season, the latter peak being more marked and the former coinciding with the period of maximum conidium liberation.In dry weather the number of ascospores increased during the night to a maximum at 06.00 h, and decreased to a low level during the day. On rainy days heavy ascospore discharge also occurred during the day. Ascospore concentration decreased significantly after dawn on sunny days whilst on overcast days the concentration remained high most of the day. Conidium production was highest around 10.00 h and decreased towards the evening to a low level during the night, reaching a minimum at 07.00 h. I N T R O D U C T I O NMicrocyclus ulei (P. Henn.) Arx, the cause of South American leaf blight of Hevea brasiliensis Muell. Arg., produces conidial lesions on young leaves at an early stage of infection; if the leaves do not fall, perithecia are formed when they are mature. The dispersal of conidia was studied by Holliday (1969); the release and dispersal of ascospores, as well as observations on dissemination of conidia, are described in the present paper. MATERIALS A N D METHODSA Hirst spore trap was set up in a nursery of young Hevea buddings at the University of the West Indies field station in north-western Trinidad in the same location as described by Holliday (1969). Apart from the original susceptible plants (clones RRIM 501 and RRIM 605, and local Verdant Vale seedlings) used by Holliday, a further 3000 susceptible buddings were added to the nursery in this study. The plants were regularly pruned during the year to ensure a continuous supply of young and old leaves.The orifice of the trap was 200 cm above ground, and sampling at a normal suction rate of ~o l / m i n took place between 2 May 1973 and z May 1975. There was no

Influence of host resistance and phenology on South American leaf blight of the rubber tree with special consideration of temporal dynamics

“…So far, it is not known whether the different susceptibilities between clones also involve the time taken for perithecia to mature, and their viability, along with the quantity of ascospores formed, and their viability. For a pathogen such as M. ulei, whose survival in unfavourable seasons and dissemination are generally attributed to sexual structures (Holliday 1970;Chee 1976c), it will be essential to determine the conditions required to achieve that phase of the disease cycle, taking into account clonal and environmental effects.…”

Role of ascospores and conidia in the initiation and spread of South American leaf blight in a rubber tree plantation

“…In the current study, the initiation of SALB in a previously healthy plot was induced by a massive arrival of exogenous ascospores, which were released throughout the year, even during the dry season, as observed in Trinidad by Chee (). Ascospores therefore play an essential role in the conservation of the fungus and in long‐distance spread of the disease to healthy zones.…”

A rubber tree’s durable resistance to Microcyclus ulei is conferred by a qualitative gene and a major quantitative resistance factor

“…This disease is widespread in the entirety of Communicated by D. Grattapaglia tropical America, from the southern region of Brazil to the south of Mexico, but it has not spread to other regions of rubber tree cultivation. Young leaves are infected by spores of M. ulei and rapidly develop large and numerous sporulating lesions that contribute to the epidemic disease expansion (Chee 1976). On susceptible cultivars, infected leaves fall and are replaced within a few weeks by new ones that can also succumb to SALB attacks (Chee and Holliday 1986).…”