2017 ASHS Annual Conference

Tissue-cultured, virus-tested plantlets of three sweetpotato cultivars (Okinawan, 0821P, and Murasaki-29) were obtained from Louisiana State UniversityAgricultural Center. There were two objectives to the field trials: 1) to compare ‘Okinawan’ obtained from a commercial field with tissue-cultured ‘Okinawan’; and 2) to compare three tissue-cultured sweetpotato cultivars. A plot consisted of three hills that were 1.5 x 9.1 m. Cuttings of commercial ‘Okinawan’ were planted at a spacing of 0.3 m in all three hills. Three tissue-cultured cultivars were planted at a spacing of 0.3 m in one hill per cultivar. Treatments (tissue-cultured vs. commercial) were blocked four times in a randomized complete block design. Cover crops were planted between the experimental plots to prevent or retard movement of insects that could carry viruses between experimental plots. At the Kula Agricultural Park on the Island of Maui, two trials were planted on October 2015 and August 2016, and harvested 4 to 5 months later. Storage roots were graded according to State of Hawaii standards, and categorized as Grade AA, A, B, and off-grade. Marketable yields combined storage roots in Grades AA, A, and B. In addition, injuries of storage roots in each category were estimated due to infestations of sweetpotato weevil [Cylas formicarius elegantulus (Coleoptera: Brentidae)]. In both trials, fresh weights of marketable storage roots of tissue-cultured ‘Okinawan’ were almost twice those of commercial ‘Okinawan’. It is uncertain whether this effect was due to a superior genotype of ‘Okinawan’ placed into tissue-culture or whether it was due to viruses reducing yields in commercial ‘Okinawan’. In both field trials, tissue-cultured cultivars differed significantly in fresh weights of marketable storage roots. In the first field trial, ‘0821P’ had 1.6 to 1.7 times greater fresh weight of marketable storage roots (20,297 kg ha^-1) compared to the other two cultivars (12,342 and 11,770 kg ha^-1, for ‘Murasaki’ and ‘Okinawan’, respectively). In the second field trial, ‘Okinawan’ had 1.7 times greater marketable storage roots (16,408 kg ha^-1) compared to ‘Murasaki’ (9,471 kg ha^-1), but did not differ from ‘0821P’ (14,134 kg ha^-1). In both trials, 0821P had significantly greater injury due to sweetpotato weevil (17 to 31%) compared to the other two cultivars (0 to 6%), perhaps due to its growth habit of tight clusters of storage roots located near the soil surface. Results from these two field trials indicate that use of virus-tested, tissue-cultured planting materials could significantly increase yields of ‘Okinawan’.