Ceratocystis fimbriata alters root system architecture and causes symptom development only in detached storage roots in Bayou Belle and Beauregard sweet potato

Little is known about how the sweet potato (Ipomoea batatas) root system responds to Ceratocystis fimbriata in the growth substrate. Understanding whether the fungus affects the root system before harvest of storage roots (SR) could guide timing of management efforts. Cuttings of cultivars Bayou Belle and Beauregard, both previously considered susceptible to black rot, were in unamended or infested sand. At the onset of SR formation, effects on first- and second-order lateral root (LR) length and number among and within treatments, cultivars and replicate experiments were recorded. First-order LR length in inoculated Bayou Belle plants was 31% greater than in inoculated plants of cultivar Beauregard in Expt 1, but there were no differences in Expt 2. Second-order LR length varied among, and within, cultivars, inoculum treatments and experiments in Expts 1 and 2. At 49 days after planting in Expt 1, only inoculated plants had necrotic lesions on stems in both cultivars, with more than twice as many recorded on Bayou Belle than Beauregard. SR had no lesions at harvest. Detached SR originating from inoculated treatments and stored in sampling bags for 25 days developed black rot lesions at either end of the SR (45% and 31% of total in Expt 1 and Expt 2, respectively) or elsewhere, including those centred on LR emergence sites or lenticels (55% and 69%, respectively). Exposing developing plants to inoculation may reveal differences in SR susceptibility not found when harvested SR are wounded and inoculated

Field performance of tissue-cultured, virus-tested ‘okinawan’ sweetpotato and comparison with some promising cultivars in hawai’i

Tissue-cultured, virus-tested (TC) plantlets of sweetpotato (Ipomoea batatas var. batatas) cultivars Okinawan, LA 08-21p, and Murasaki-29 were obtained from Louisiana State University Agricultural Center. The objectives of field trials conducted at the Kula Agricultural Park, Maui, HI, were to compare yield and pest resistance of 1) ‘Okinawan’ obtained from a commercial (C) field with TC ‘Okinawan’ and 2) TC Okinawan with the aforementioned TC cultivars. Trials were planted Oct. 2015 and Aug. 2016 and harvested 5 months later. Storage roots were graded according to State of Hawai’i standards, and marketable yields included Grades AA, A, and B. In addition, injuries due to sweetpotato weevil (Cylas formicarius elegantulus) or rough sweetpotato weevil (Blosyrus asellus) were estimated. In both trials, fresh and dry weights of marketable storage roots of TC ‘Okinawan’ were nearly twice those from commercial planting material. In both trials, marketable fresh weights differed among the three TC cultivars; however, significant interactions were found, indicating that yields of cultivars differed between years. In the first field trial, ‘LA 08-21p’ had fresh marketable yields 1.6 to 1.7 times greater than TC ‘Okinawan’ and Murasaki-29, respectively. In the second trial, fresh marketable yields of TC ‘Okinawan’ and ‘LA 08-21p’were similar and 1.7 to 1.5 times greater than that of ‘Murasaki-29’, respectively. In both trials, ‘LA 08-21p’ had greater sweetpotato weevil injury than did the other two cultivars. Interestingly, in the second year, TC ‘Okinawan’ had greater rough sweetpotato weevil injury than did the other cultivars. Our results indicate that tissue-cultured planting materials increased marketable yields of TC ‘Okinawan’ compared with C ‘Okinawan’ sweetpotato and that the other TC cultivars did not produce greater yields than TC Okinawan

Estimativa das temperaturas cardinais e modelagem do desenvolvimento vegetativo em batata-doce

Objetivou-se, neste trabalho, determinar as temperaturas cardinais da batata-doce e comparar a simulação da emissão de nós com o modelo do plastocrono (linear) e com o modelo de Wang e Engel (não linear) além da melhor forma de entrada da temperatura do ar nos modelos. A calibração e o teste dos modelos foram feitos pelos dados de número de nós na haste principal de plantas de batata-doce, cultivar Princesa, coletados em experimentos conduzidos em Santa Maria, RS, Brasil, em sete épocas de plantio, nos anos 2010, 2011 e 2012. Melhor predição dos modelos foi obtida com o uso das temperaturas cardinais 12, 30 e 40 ºC. Os modelos plastocrono e Wang e Engel apresentaram desempenho semelhante. A versão com a temperatura média foi superior às temperaturas mínima e máxima, em ambos os modelos. Os dois modelos podem ser utilizados para simular o desenvolvimento vegetativo da batata-doce quando cultivada na época recomendada. Sugere-se, fora deste período, o uso do modelo de Wang e Engel

Variation in virus symptom development and root architecture attributes at the onset of storage root initiation in 'beauregard' sweetpotato plants grown with or without nitrogen.

It has been shown that virus infections, often symptomless, significantly limit sweetpotato productivity, especially in regions characterized by low input agricultural systems. In sweetpotatoes, the successful emergence and development of lateral roots (LRs), the main determinant of root architecture, determines the competency of adventitious roots to undergo storage root initiation. This study aimed to investigate the effect of some plant viruses on root architecture attributes during the onset of storage root initiation in 'Beauregard' sweetpotatoes that were grown with or without the presence of nitrogen. In two replicate experiments, virus-tested plants consistently failed to show visible symptoms at 20 days regardless of nitrogen treatment. In both experiments, the severity of symptom development among infected plants ranged from 25 to 118% when compared to the controls (virus tested plants grown in the presence of nitrogen). The presence of a complex of viruses (Sweet potato feathery mottle virus, Sweet potato virus G, Sweet potato virus C, and Sweet potato virus 2) was associated with 51% reduction in adventitious root number among plants grown without nitrogen. The effect of virus treatments on first order LR development depended on the presence or absence of nitrogen. In the presence of nitrogen, only plants infected with Sweet potato chlorotic stunt virus showed reductions in first order LR length, number, and density, which were decreased by 33%, 12%, and 11%, respectively, when compared to the controls. In the absence of nitrogen, virus tested and infected plants manifested significant reductions for all first order LR attributes. These results provide evidence that virus infection directly influences sweetpotato yield potential by reducing both the number of adventitious roots and LR development. These findings provide a framework for understanding how virus infection reduces sweetpotato yield and could lead to the development of novel strategies to mitigate virus effects on sweetpotato productivity

Detection of Ty1-copia-like reverse transcriptase sequences in Ipomoea batatas (L.) Poir

Ty1-copia-like sequences were PCR amplified from sweetpotato [Ipomoea batatas (L.) Poir.] L87-95 genomic DNA samples by using Ty1-copia reverse transcriptase-specific primers. PCR fragments within the expected size range were isolated, cloned, and sequenced. Inferred amino acid sequences of two randomly selected cloned fragments were found to be highly homologous to Ty1-copia-like reverse transcriptase sequences in the GenBank database. Subsequent sequencing of an additional 22 cloned fragments revealed a high level of reverse transcriptase sequence diversity (sequence divergence ranged from 2% to 73%). Southern blot hybridization analysis indicated that these sequences are present in the genome of I. batatas and taxonomic relatives in high copy numbers. PCR amplification from leaf cDNA obtained from a sweetpotato clone using Ty1-copia reverse transcriptase-specific primers yielded a Ty1-copia-like fragment. This is the first known report of the presence of genomic, and putatively expressed, Ty1-copia-like reverse transcriptase sequences in I. batatas