EVALUATION OF A BIOASSAY FOR SCREENING RESISTANCE OF PINEAPPLE TO ROOT-KNOT AND RENIFORM NEMATODE

Accurate greenhouse bioassays of root-knot and reniform nematode resistance in pineapple have required 9 to 12 months. We developed protocols to evaluate pineapple for resistance to nematodes using a reproductive factor (Rf=Pf/Pi) that shortened this time to 3 months for Meloidogyne javanica and to 6 months for Rotylenchulus reniformis. We used pineapple plants that had been subjected to a genetic modification procedure using a cystatin gene. Plants were transitioned from tissue culture to the greenhouse by repotting into individual pots and allowing 1 month for growth before inoculation with nematodes. This protocol was used for eight different sets of plants containing multiple pineapple lines. Tissue-cultured plants of ‘Smooth Cayenne’ clone Champaka F-153 and hybrid D-10 that had not been subjected to the transformation protocol were used as controls. The Rf of M. javanica and R. reniformis on untransformed D-10 averaged 5.8 (s=10.28, n=144) and 37.8 (s=59.19, n=64), respectively. On F153, the Rf was 32.9 (STD=37.17, n=13) for R. reniformis. For those plants that had been subjected to a transformation process, M. javanica Rf averaged 20.68 (s=35.57, n=389) and R. reniformis Rf averaged 41.72 (s=70.88, n=332) over all of the pineapple lines. In Line 256, the Rf of M. javanica and R. reniformis averaged 22.69 (s=21.12, n=79) and 28.47 (s=35.23, n=97), respectively. In Line 101, M. javanica Rf was 4.7 (s=6.78, n=172). The coefficient of variation associated with the Rf bioassays exceeded 100 in all cases making conclusions difficult. The sets were composed of many lines of pineapple, most represented by only a few plants. Plant size was not uniform at transplanting and plant growth among lines was different. Differences arising from the time of year the assay was conducted may also have contributed to the wide variation. The transformation and genetic modification process appears to alter the host status of pineapple, making some lines better hosts to the nematodes. Because of the variation, it is necessary to produce and evaluate multiple plants in a line to accurately identify nematode resistance. A rapid and reliable bioassay is critical for evaluation of transgenic pineapple lines as well as very useful for evaluation of non-transgenic pineapple plants.