Impatiens Downy Mildew: Pathogens, Management Options, and Genetic Resistance

摘要

Impatiens (Impatiens walleriana) and New Guinea impatiens (Impatiens hawkeri) (NGI) are very important bedding plants to the floriculture and landscape industries in Florida and many other states in the United States. Downy mildew (DM) has become a devastating disease for impatiens growers and caused significant economic damages to many segments of the floriculture and landscape industries. Three oomycete species could cause DM on impatiens, and Plasmo-para obducens has recently caused regional outbreaks of DM in the United States. This pathogen thrives in cool, moist conditions but has a narrow host range. Impatiens plants infected by P. obducens have chlorotic and downward-curling leaves, followed by leaf and flower drops, and eventually completedefoliation and plant collapsing. Several fungicides are effective to control DM when they are applied prior to disease development. Some fungicides have shown a carryover protection on plants installed in the landscape, but such protection generally didnot last beyond one month. A number of cultural practices may be used to minimize crop losses due to DM. Impatiens cultivars and their hybrids are susceptible to DM while NGI cultivars are resistant to DM. It has not been possible to transfer the DM resistance from NGI into I. walleriana due to the differences between the two species in chromosome number, size, and morphology. Several genetic strategies are available for introducing DM resistance into impatiens. A better understanding of the resistancemechanisms in NGI will be very valuable for developing DM-resistant impatiens cultivars, which will be critical for the sustainability of impatiens production in Florida and other states in the United States.