Sweet potato virus disease (SPVD) is the most devastating viral disease in sweet potato (Ipomoea batatas (L.) Lam.), causing substantial yield losses worldwide. We conducted a systemic investigation on the spread, transmission, and pathogenesis of SPVD. Field experiments conducted over two years on ten sweet potato varieties showed that SPVD symptoms first occurred in newly developed top leaves, and spread from adjacent to distant plants in the field. The SPVD incidence was mainly (but not only) determined by the resistance of the varieties planted, and each variety exhibited a characteristic subset of SPVD symptoms. SPVD was not robustly transmitted through friction inoculation, but friction of the main stem might contribute to a higher SPVD incidence rate compared to friction of the leaf and branch tissues. Furthermore, our results suggested that SPVD might be latent in the storage root. Therefore, using virus-free storage roots and cuttings, purposeful monitoring for SPVD according to variety-specific symptoms, and swiftly removing infected plants (especially during the later growth stages) would help control and prevent SPVD during sweet potato production. Comparative transcriptome analysis revealed that numerous genes involved in photosynthesis, starch and sucrose metabolism, flavonoid biosynthesis, and carotenoid biosynthesis were downregulated following SPVD, whereas those involved in monolignol biosynthesis, zeatin biosynthesis, trehalose metabolism, and linoleic acid metabolism were upregulated. Notably, critical genes involved in pathogenesis and plant defense were significantly induced or suppressed following SPVD. These data provide insights into the molecular changes of sweet potato in response to SPVD and elucidate potential SPVD pathogenesis and defense mechanisms in sweet potato. Our study provides important information that can be used to tailor sustainable SPVD control strategies and guide the molecular breeding of SPVD-resistant sweet potato varieties.

In the relay intercropping system of maize/sweet potato, the growth of the sweet potatoes is seriously limited by weak light stress in the early stage due to shade from maize plants. However, it is not clear how the weak light affects sweet potatoes and causes tuberous root loss. By setting two light intensity levels (weak light = 30% transmittance of normal light), this study evaluated the responses of two sweet potato cultivars with different tolerances to weak light in a field-based experiment and examined the divergence of gene expression related to light and photosynthesis in a pot-based experiment. The results showed that under weak light, the anatomic structure of functional leaves changed, and the leaf thickness decreased by 39.98% and 17.32% for Yuhongxinshu-4 and Wanshu-7, respectively. The ratio of S/R increased, and root length, root superficial area, and root volume all decreased. The photosynthetic enzyme rubisco was weakened, and the net photosynthetic rate (Pn) declined as well. The level of gene expression in Wanshu-7 was higher than that of Yuhongxinshu-4. The KEGG analysis showed that differentially expressed genes from the two cultivars under weak-light stress used the same enrichment pathway, mainly via glutathione metabolism and flavonoid biosynthesis. After full light levels were restored, the differentially expressed genes were all enriched in pathways such as photosynthesis, photosynthetic pigment synthesis, and carbon metabolism. These findings indicated that weak light changed the plant morphology, photosynthetic physiology and gene expression levels of sweet potatoes, which eventually caused losses in the tuberous root yield. The more light-sensitive cultivar (Wanshu-7) had stronger reactions to weak light. This study provides a theoretical basis and strategy for breeding low-light-tolerant varieties and improving relay intercropping production in sweet potatoes.

Seedling cultivation is the foremost part of sweet potato (Ipomoea batatas L. Lam) production. It is of great significance to reveal the effects of different temperatures on the nutrients of sweet potato storage roots and their relationship with the sprouting quality and to explore the appropriate temperature management for seedlings. In this study, we simulated the temperature differences during the sprouting and seedling period in the summer growing area of sweet potato in the Yangtze River Basin and set three constant temperatures (17 °C, 22 °C and 27 °C) and corresponding three-day/night variable temperatures (21/13 °C, 26/18 °C and 31/23 °C). Thus, we investigated the nutrients, amylase activity, endogenous hormones, and sprouting characteristics of storage roots during the sprouting and seedling period of three sweet potato cultivars with different starch contents. The results showed that with the increase in temperature, the starch and soluble protein (SP) contents in sweet potato storage roots decreased, and the total soluble sugar (TSS), reducing sugar (RS), and sucrose contents increased during the sprouting and seedling period. The amylase activity enhanced; the hormone (IAA) content increased, and the abscisic acid (ABA) content decreased, which, in turn, led to an earlier time of sprouting time (ST), emergence stage (ES), and full stand of seedling stage (FSS). Comparing at the same average temperature, the physiological metabolism and sprouting time and quality of sweet potato were better at variable temperatures than at constant temperatures, in which 31/23 °C was more conducive to the advancement of the ST of sweet potato. At the same time, it was more conducive to the improvement of the seedling cutting amount (SCA), seedling weight (SDW), and seedling number (SDN). The sprouting time and quality of different sweet potato cultivars differed, and cultivars with higher starch content were superior to those with lower starch content. The sucrose and starch contents at different sprouting stages of storage roots can be used as important indicators of the quality of sweet potato seedlings.

Sweet potato virus disease (SPVD) is one of the main virus diseases in sweet potato [Ipomoea batatas (L.) Lam] that seriously affects the yield of sweet potato. Therefore, the establishment of a simple, rapid and effective method to detect SPVD is of great significance for the early warning and prevention of this disease. In this study, the experiment was carried out in two years to compare the grafting method and side grafting method for three sweet potato varieties, and the optimal grafting method was selected. After grafting with seedlings infected with SPVD, the symptomatic diagnosis and serological detection were performed in 86 host varieties, and the differences in SPVD resistance were determined by fluorescence quantitative PCR (qRT-PCR) and nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA). The results showed that the survival rate of grafting by insertion method was significantly higher than that by side grafting method, and the disease resistance of different varieties to sweet potato virus disease was tested. The detection method established in this study can provide theoretical basis for identification and screening of resistant sweet potato varieties.

Sweet potato/maize relay-cropping mode is considered as the main farming practices of dry land in Southwest China. Although relay-cropping would cause the reduction of fresh tuber yield, it still remained unclear that the reason was shade resulted from maize or genotype of sweet potato. The present work aims at exploring the effects of maize (Zea mays L.) plant-type on photosynthetic physiology and yield of sweet potato (Ipomoea balatas L.) in relay-cropping system. Besides, three plant-types maize cultivars including compact, semi-compact and expanded type were used for relay-cropping with different sweet potato cultivars (‘Yushu-2’, ‘Yushu-6’ and ‘Nanshu-88’) in field. The results showed that the photosynthetically active radiation (PAR) was declined with the increase of expansion of maize plant-type, which decreased by 77.5%, 80.1% and 82.1% respectively. When relay-cropped with extended maize, the yield reduction rate of sweet potato was the highest (67%). The shade-resistance of different genotype of sweet potatoes was different, and the yield reduction rate of ‘Yushu-2’ was the lowest (37.01%). Through conducting correlations analysis, it showed that fresh tuber yield had significant positive correlation with Effective Quantum Yield (Y(II)) and significant negative correlation with Non Photochemical Quenching Coefficient (NPQ). In terms of ‘Yushu-2’, the proportion of heat dissipation was the lowest, and its light quantum efficiency was higher than others. As a result, its reduction rate of yield was lower than the other two. We suggested that compact maize cultivar relay-cropping with strong shade-resistance sweet potato cultivar should be mainly applied in practice of sweet potato.

Sweet potato (Ipomoea batatas L.) relay intercropping with maize exposes sweet potato to weak levels of sunlight due to the shadow maize creates during the symbiotic period. The insufficient light accordingly causes slow growth and development of vines and leaves of sweet potato in its early stage. The planting density and row direction of maize, the width of the intercropping strip, and the lodging type of sweet potato may form various photo conditions that influence sweet potato. The objective of this experiment was to research the effects of different ridging types on sweet potato and to elucidate the mechanisms of ecological conditions, photosynthetic physiology and intercropping benefits. The results indicated that, contrast to the one wide-ridge with planting two rows of sweet potato and two narrow ridges with planting two rows, mound planting was more superior in many aspects. Through mound planting sweet potato showed a larger range of temperature in air and soil, higher net photosynthetic rate, more active enzymes related with photosynthesis, and more benefits of relay intercropping.