An Analysis of the Quantitative and Qualitative Composition of the Nematode Populations in Pineapple Fields in Puerto Rico

Abstract

In this study undertaken in Puerto Rico during the months from March through September 1957, 60 different samples of plant-parasitic nematodes from roots and soil were taken from various pineapple farms in 3 of the 4 production Regions of Puerto Rico: Northern, Southwestern, and Central. The fields were selected at random, and those showing no symptoms of nematode injury, as well as those showing such symptoms, were studied. The methods employed for field collection were a modification of those used by Cobb. The laboratory methods and the recovery of nematodes from the soil were a combination of the screen and Baermann-funnel methods. Twenty-three different genera of nematodes were recovered, 16 of which were recognized as being plant parasites and the other 7 were suspected. There was no case in which a sample was found to be free of plant nematodes. In fact, the lowest number of genera present in 1 sample was 5 and the highest was 15, with a mean average of 9 genera per sample. The most frequently occurring genera were Rotylenchulus and Helicotylenchus which were present in all the samples. Less frequent but still common were Pratylenchus, Paratylenchus, Aphelenchoides, Dorylaimus, Ditylenchus, and Meloidogyne. This last one was found only in the Northern Region. The other 16 genera were less widely distributed. Populations of the first 2 genera were large, with a general mean average of 0.97 and 0.67 million per square meter (3.90 and 2.70 billions per acre), respectively. Their population size was higher in the Northern Region, while in the Central and Southwestern Regions it was lower. The average nematode population was 1.75 millions per square meter (7.05 billions per acre) at 6 inches depth. Several edaphic, climatological, and biological factors were found to be related to population sizes for all the genera and some specific genera studied. Population size of the genera varied with geographic location, type of soil, age and variety of the plants (although not statistically), previous crops planted, and temperature. No apparent relation was noted between precipitation except for the root-knot nematode and pH of the soil and nematode population size. No study was conducted of other biological factors such as different soil organisms, or cultivation methods and soil additives. It was estimated from the results obtained in this study and the damage observed in the pineapple plantings of this as well as previously scattered experiments that nematodes cause the loss of a great part of the crop yield in the Island. This loss has been calculated by the Extension Service officers to amount to at least 40 percent of the potential yield.