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Production and maintenance of virus‐free planting materials is pivotal for the control of viral diseases. The present study attempted to test exogenous application of melatonin for eradication of apple stem grooving virus (ASGV) from virus‐infected in vitro shoots of apple cultivar Gala. Exogenous application of 15 μm melatonin to the shoot proliferation medium significantly increased the number of shoots and shoot length. The level of endogenous indole‐3‐acetic acid (IAA) was the highest in the shoots proliferating on the shoot proliferation medium containing 15 μm melatonin. Shoot regrowth levels were significantly higher in shoot tips of the virus‐infected shoots cultured for 4 weeks on this medium than the control. In addition, culture of shoot tips of the virus‐infected in vitro shoots proliferated for 4 weeks on this medium resulted in 95% of shoots being virus‐free, while no virus‐free shoots were obtained in shoot tips of the virus‐infected shoots cultured without melatonin. Analyses by microtissue direct RT‐PCR and RT‐qPCR showed that ASGV concentration decreased in shoot tips of the virus‐infected shoots proliferating on the medium containing 15 μm melatonin for 4 weeks. Virus localization showed that exogenous application of melatonin enlarged the virus‐free area in the virus‐infected shoot tips. These data provide explanations as to why exogenous application of melatonin can efficiently eradicate ASGV. Exogenous application of melatonin provides an alternative means for plant virus eradication and has the potential to produce virus‐free plants. [ABSTRACT FROM AUTHOR]

A non-probabilistic reliability optimization method for structures with uncertain-but-bounded variables was presented. Based on the interval model description for the uncertain-but-bounded parameters, the non-probabilistic reliability index was used to measure the structural reliability. The optimal design was formulated as a nested two-loop optimization problem. For a nonlinear function, a number of constraints that satisfied the non-probabilistic reliability index were treated as the serial system, and the feasible region of the uncertain parameters was determined by the target non-probabilistic reliability index. The inner optimization method for solving a number of non-probabilistic reliability indices was transformed into the problem of minimizing the functions within the feasible range. For a linear function, the non-probabilistic reliability optimization problem can be transformed into a deterministic optimization problem. The high computational cost of determining the non-probabilistic reliability was greatly reduced. Three numerical examples were presented to illustrate the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This study attempted to eradicate Apple stem pitting virus (ASPV) and Apple stem grooving virus (ASGV) from virus-infected in vitro shoots of apple rootstocks 'M9' and 'M26' using shoot tip culture and cryopreservation. In shoot tip culture, shoot tips (0.2 mm in length) containing two leaf primordia failed to show shoot regrowth. Although shoot regrowth rate was the highest in the largest shoot tips (1.0 mm in length) containing four leaf primordia, none of the regenerated shoots was virus-free. Shoot tips (0.5 mm in length) containing two and three leaf primordia produced 100% and 10% of ASPV-free shoots, respectively, while those (1.0 mm) containing four leaf primordia were not able to eradicate ASPV. ASGV could not be eradicated by shoot tip culture, regardless of the size of the shoot tips tested. In cryopreservation, shoot tips (0.5 mm in length) containing two leaf primordia did not resume shoot growth. Although 1.0-mm and 1.5-mm shoot tips gave similarly high ASPV-free frequencies, the latter had much higher shoot regrowth rate than the former. Very similar results of shoot regrowth and virus eradication by shoot tip culture and cryopreservation were observed in both 'M9' and 'M26'. Histological observations showed that only cells in upper part of apical dome and in leaf primordia 1-3 survived, while other cells were damaged or killed, in shoot tips following cryopreservation. Virus immunolocalization found ASPV was not detected in upper part of apical dome and leaf primordia 1 and 2, but was present in lower part of apical dome, and in leaf primordium 4 and more developed tissues in all samples tested. ASPV was also detected in leaf primordium 3 in about 16.7% and 13.3% samples tested in 'M9' and 'M26'. ASGV was observed in apical dome and leaf primordia 1-6, leaving only a few top layers of cells in apical dome free of the virus. Different abilities of ASPV and ASGV to invade leaf petioles and shoot tips were also noted. [ABSTRACT FROM AUTHOR]