Interactions Between Rotylenchus reniformis and Pineapple mealybug wilt associated virus-1 in Pineapple

Pineapple, Ananas comosus (L.) Merr., is a perennial, xerophytic monocot in the Bromeliaceae family (13). Planting materials used for commercial production are typically the crown from the top of the fruits (19). The planted crowns, referred to as the plant crop, will each produce a single pineapple fruit 18 to 20 months after planting (19). Following plant crop harvest, a ratoon crop develops from suckers produced on the stem of the plant crop plants (13). Fruit from the ratoon crop is harvested in approximately 12 to 15 months (19). Pineapple can be affected by many different pests and pathogens (20). Among the most serious are plant-parasitic nematodes and the complex of closteroviruses associated with mealybug wilt of pineapple (MWP). Rotylenchus reniformis and Meloidogyne javanica are the major plant-parasitic nematodes that occur throughout the pineapple growing areas of Hawaii (20). R. reniformis reduces plant crop yields (30,31) and devastates first ratoon crops (20). Effects of the nematodes are mitigated by an intercycle fallow, preplant soil fumigation, and postplant nematicide applications (30). Mealybug wilt nearly destroyed the Hawaiian pineapple industry in the early 1900s (3) and continues to pose a threat to yields (7,8,21,25,27). Two distinct closteroviruses have been found in pineapple plants from Hawaii and around the world (10,15,24,26,28,34). The incidence of Pineapple mealybug wilt associated virus-1 (PMWaV-1) varies from 20 to100% in healthy-appearing Hawaiian-grown proprietary selections (9,28). Infection incidences of PMWaV-2 are lower, ranging from 0 to 36% in the same selections (28). Crowns collected from these selections are used to establish plant crops and, if infected with PMWaVs, serve as a primary virus source in the field. Infections have been perpetuated through this clonal propagation of pineapple for decades (9,28). Both PMWaV-1 and PMWaV-2 are mealybug-transmitted (24,26,29). PMWaV-2 and mealybugs both play a role in MWP symptom induction, whereas PMWaV-1 does not appear to be necessary for symptom development (8,24,26). Although PMWaV-1 infection may not be directly involved in MWP, its presence correlates with growth reduction in the plant crop (23) and reduces fruit yield in the ratoon crop (25,27). Nematodes and virus infection each affect the profitability and continued cultivation of pineapple in Hawaii. Impacts of interactions between plant stresses are not uncommon. Nematode interactions with fungi, bacteria, and viruses have been documented to synergistically elicit certain diseases in some species. For example, Meloidogyne and Fusarium together can exacerbate wilts of cotton and tobacco (4,14,32), and Criconemella and Pseudomonas syringae pv. syringae cause short life of peach trees (18). PMWaV-1 infection has a greater reduction on ratoon crop yield in the presence of environmental stress such as drought (25). We investigated the effects of PMWaV-1 infection on R. reniformis populations under greenhouse conditions and evaluated the effects of these two pathogens together on pineapple growth, fruit maturation date, and yield in a commercial pineapple field.