Effect of varying UAV height on the precise estimation of potato crop growth.

A phenotyping pipeline utilising DeepLab was developed for precisely estimating the height, volume, coverage and vegetation indices of European and Japanese varieties. Using this pipeline, the effect of varying UAV height on the precise estimation of potato crop growth properties was evaluated. A UAV fitted with a multispectral camera was flown at a height of 15 m and 30 m in an experimental field where various varieties of potatoes were grown. The properties of plant height, volume and NDVI were evaluated and compared with the manually obtained parameters. Strong linear correlations with R2 of 0.803 and 0.745 were obtained between the UAV obtained plant heights and manually estimated plant height when the UAV was flown at 15 m and 30 m respectively. Furthermore, high linear correlations with an R2 of 0.839 and 0.754 were obtained between the UAV-estimated volume and manually estimated volume when the UAV was flown at 15 m and 30 m respectively. For the vegetation indices, there were no observable differences in the NDVI values obtained from the UAV flown at the two heights. Furthermore, high linear correlations with R2 of 0.930 and 0.931 were obtained between UAV-estimated and manually measured NDVI at 15 m and 30 m respectively. It was found that UAV flown at the lower height had a higher ground sampling distance thus increased resolution leading to more precise estimation of both the height and volume of crops. For vegetation indices, flying the UAV at a higher height had no effect on the precision of NDVI estimates.

A survey of metabolic changes in potato leaves by NMR-based metabolic profiling in relation to resistance to late blight disease under field conditions.

Non-targeted nuclear magnetic resonance (NMR)-based metabolic profiling was applied to potato leaves to survey metabolic changes associated with late blight resistance under field conditions. Potato plants were grown in an experimental field, and the compound leaves with no visible symptoms were collected from 20 cultivars/lines at two sampling time points: (i) the time of initial presentation of symptoms in susceptible cultivars and (ii) 12 days before this initiation. 1 H NMR spectra of the foliar metabolites soluble in deuterium oxide- or methanol-d4 -based buffers were measured and used for multivariate analysis. Principal component analysis for six cultivars at symptom initiation showed a class separation corresponding to their levels of late blight resistance. This separation was primarily explained by higher levels of malic acid, methanol, and rutin and a lower level of sucrose in the resistant cultivars than in the susceptible ones. Partial least squares regression revealed that the levels of these metabolites were strongly associated with the disease severity measured in this study under field conditions. These associations were observed only for the leaves harvested at the symptom initiation stage, but not for those collected 12 days beforehand. Subsequently, a simple, alternative enzymatic assay for l-malic acid was used to estimate late blight resistance, as a model for applying the potential metabolic marker obtained. This study demonstrated the potential of metabolomics for field-grown plants in combination with targeted methods for quantifying marker levels, moving towards marker-assisted screening of new cultivars with durable late blight resistance. Copyright © 2016 John Wiley & Sons, Ltd.

Molecular characterization of the bacterial community in a potato phytosphere.

The bacterial community of a potato phytosphere at the flowering stage was examined using both culture-dependent and -independent methods. Tissues (leaves, stems, roots and tubers) were sampled from field-grown potato plants (cultivar Matilda), and the clone libraries of 16S rRNA genes and the isolate collections using R2A medium were constructed. By analyzing the combined data set of 16S rRNA gene sequences from both clone libraries and isolate collections, 82 genera from 8 phyla were found and 237 OTUs (≥97% identity) at species level were identified across the potato phytosphere. The statistical analyses of clone libraries suggested that stems harbor the lowest diversity among the tissues examined. The phylogenetic analyses revealed that the most dominant phylum was shown to be Proteobacteria for all tissues (62.0%-89.7% and 57.7%-72.9%, respectively), followed by Actinobacteria (5.0%-10.7% and 14.6%-39.4%, respectively). The results of principal coordinates analyses of both clone libraries and isolate collections indicated that distinct differences were observed between above- and below-ground tissues for bacterial community structures. The results also revealed that leaves harbored highly similar community structures to stems, while the tuber community was shown to be distinctly different from the stem and root communities.

DNA marker-assisted evaluation of potato genotypes for potential resistance to potato cyst nematode pathotypes not yet invading into Japan.

One of major objectives of crop breeding is conferring resistance to diseases and pests. However, large-scale phenotypic evaluation for many diseases and pests is difficult because strict controls are required to prevent their spread. Detection of disease resistance genes by using DNA markers may be an alternative approach to select potentially resistant accessions. Potato (Solanum tuberosum L.) breeders in Japan extensively use resistance gene H1, which confers nearly absolute resistance to potato cyst nematode (Globodera rostochiensis) pathotype Ro1, the only pathotype found in Japan. However, considering the possibility of accidental introduction of the other pathotypes, breeding of resistant varieties is an important strategy to prevent infestation by non-invading pathotypes in Japan. In this study, to evaluate the prevalence of resistance genes in Japanese genetic resources, we developed a multiplex PCR method that simultaneously detects 3 resistance genes, H1, Gpa2 and Gro1-4. We revealed that many Japanese varieties possess not only H1 but Gpa2, which are potentially resistant to other pathotypes of potato cyst nematode. On the other hand, no genotype was found to have the Gro1-4, indicating importance of introduction of varieties having Gro1-4. Our results demonstrate the applicability of DNA-marker assisted evaluation of resistant potato genotypes without phenotypic evaluation.

Effects of storage temperature on the contents of sugars and free amino acids in tubers from different potato cultivars and acrylamide in chips.

To clarify the effects of storage temperature on potato components and acrylamide in chips, tubers from five cultivars were stored at various temperatures (2, 6, 8, 10, and 18 degrees C) for 18 weeks, and the contents of sugars, free amino acids in tubers, and acrylamide in chips after frying were analyzed. At temperatures lower than 8 degrees C, the contents of reducing sugars increased markedly in all cultivars, with similar increases in the acrylamide level and dark brown chip color. Free amino acids showed little change at the storage temperatures tested and varied within certain ranges characteristic of each cultivar. The contents of reducing sugars correlated well with the acrylamide level when the fructose/asparagine molar ratio in the tubers was <2. When the fructose/asparagine ratio was >2 by low-temperature storage, the asparagine content, rather than the reducing sugar content, was found to be the limiting factor for acrylamide formation.

Effect of the dates of extraction on the quality of potato pulp.

The objectives of this study were to evaluate the fundamental properties of potato pulp and to explore its potential uses. Lactic acid bacteria were the dominant microbes in potato pulp over the season (maximum being 10(8)/g). The water content in potato pulp was approximately 80% in all season. Starch and fiber were the main components of potato pulp, amounting to 80% of the dried matter regardless of the season. The fermentation of potato pulp by Rhizopus oryzae progressed only in the potato pulp extracted at the end of the season. This indicated that the fermentation of potato pulp was influenced by the dates of extraction, and it was assumed that the quality of the components, such as pectin, varied with such dates.

Change in content of sugars and free amino acids in potato tubers under short-term storage at low temperature and the effect on acrylamide level after frying.

Changes in the sugar and amino acid contents of potato tubers during short-term storage and the effect on the acrylamide level in chips after frying were investigated. The acrylamide content in chips began to increase after 3 days of storage at 2 degrees C in response to the increase of glucose and fructose contents in the tubers. There was strong correlation between the reducing sugar content and acrylamide level, R(2)=0.873 for fructose and R(2)=0.836 for glucose. The sucrose content had less correlation with the acrylamide content because of its decrease after 4 weeks of storage at 2 degrees C, while the reducing sugar in potato tubers and the acrylamide in chips continued to increase. The contents of the four amino acids, i.e., asparatic acid, asparagine, glutamic acid and glutamine, showed no significant correlation with the acrylamide level. These results suggest that the content of reducing sugars in potato tubers determined the degree of acrylamide formation in chips. The chip color, as evaluated by L* (lightness), was correlated well with the acrylamide content.

Roots of Pisum sativum L. exhibit hydrotropism in response to a water potential gradient in vermiculite.

In the present study, root hydrotropism in an agravitropic mutant of Pisum sativum L. grown in vermiculite with a steep water potential gradient was examined. When wet and dry vermiculite were placed side by side, water diffused from the wet (-0.04 MPa) to the dry (-1.2 MPa) and a steep water potential gradient became apparent in the dry vermiculite close to the boundary between the two. The extent and location of the gradient remained stable between the fourth and sixth day after filling a box with vermiculite, and the steepest gradient (approx. 0.02 MPa mm-1) was found in the initially dry vermiculite between 60 and 80 mm from the boundary. When seedlings with 25-35 mm long roots were planted in the initially dry vermiculite near where the gradient had been established, each of the main roots elongated toward the wet vermiculite, i.e. toward the high water potential. Control roots elongated without curvature in both the wet and the dry vermiculite, in which no water potential gradient was detectable. These results show that pea roots respond to the water potential gradient around them and elongate towards the higher water potential. Therefore, positive hydrotropism occurs in vermiculite just as it does in air. Hydrotropism in soil may be significant when a steep water potential gradient is apparent, such as when drip irrigation is applied.