[Control of continuous potato monoculture barrier via biological soil disinfestation method in Yellow River irrigation areas of central Gansu Province, Northwest China].

The potential of biological soil disinfestation (BSD) in control of continuous potato monoculture barrier was investigated in present study. BSD involves the induction of soil reduction conditions through incorporation of easily decomposed organic materials into soil, flooding the soil by irrigation, and covering the soil surface with plastic film. Control (CK) was left without cover and organic amendment as well as flooding. Field experiment was conducted for testing the effect of BSD approach on the control of continuous potato monoculture barrier, especially on tube yield, plant growth and development, suppression of soil-borne pathogen, and soil microbial community and enzyme activities. Compared with CK, BSD treatment significantly increased tuber yield by 16.1% and plant biomass by 30.8%, respectively. Meanwhile, the incidence of diseased plant and the ratio of diseased tuber in BSD treatment also significantly decreased by 68.0% and 46.7% as compared to those in CK, respectively. BSD treatment significantly increased the content of chlorophyll and branch numbers per main stem of potato plants, improved the morphological characteristics of potato root system. In the course of BSD before potato sowing, soil pH value and bacteria/fungi significantly increased, but populations of fungi and Fusarium sp. significantly decreased compared with CK. There were no significant changes in populations of bacteria and actinomycetes between CK and BSD treatments. During potato growing stage, the populations of both soil fungi and Fusarium sp. were lower in BSD treatment than those of CK. With the advance of potato growth, the population of Fusarium sp. in BSD treatment gradually increased compared with CK. There were no significant changes in soil enzyme activities in the course of BSD before potato sowing and the whole of potato growing stage. It was concluded that BSD has the potential to control continuous potato monoculture barrier and may be an important element in a sustainable and effective management strategy for potato soil-borne diseases.

Ultrastructural and physiological responses of potato (Solanum tuberosum L.) plantlets to gradient saline stress.

Salinity is one of the major abiotic stresses that impacts plant growth and reduces the productivity of field crops. Compared to field plants, test tube plantlets offer a direct and fast approach to investigate the mechanism of salt tolerance. Here we examined the ultrastructural and physiological responses of potato (Solanum tuberosum L. c.v. "Longshu No. 3") plantlets to gradient saline stress (0, 25, 50, 100, and 200 mM NaCl) with two consequent observations (2 and 6 weeks, respectively). The results showed that, with the increase of external NaCl concentration and the duration of treatments, (1) the number of chloroplasts and cell intercellular spaces markedly decreased, (2) cell walls were thickened and even ruptured, (3) mesophyll cells and chloroplasts were gradually damaged to a complete disorganization containing more starch, (4) leaf Na and Cl contents increased while leaf K content decreased, (5) leaf proline content and the activities of catalase (CAT) and superoxide dismutase (SOD) increased significantly, and (6) leaf malondialdehyde (MDA) content increased significantly and stomatal area and chlorophyll content decline were also detected. Severe salt stress (200 mM NaCl) inhibited plantlet growth. These results indicated that potato plantlets adapt to salt stress to some extent through accumulating osmoprotectants, such as proline, increasing the activities of antioxidant enzymes, such as CAT and SOD. The outcomes of this study provide ultrastructural and physiological insights into characterizing potential damages induced by salt stress for selecting salt-tolerant potato cultivars.

[Characteristics of dry matter and potassium accumulation and distribution in potato plant in semi-arid rainfed areas].

In 2010, a field experiment with potato (Solanum tuberosum) cultivar 'Xindaping' was conducted at the Dingxi Extension Center of Gansu Province, Northwest China, aimed to understand the accumulation and distribution patterns of dry matter (DM) and potassium (K) in the organs of potato plant in semi-arid rainfed areas. During the whole growth period of the cultivar, the DM accumulation in root, stem, and leaf all showed a unimodal curve, with the DM accumulation rate being leaf > stem > root, whereas the DM accumulation in whole plant and tuber was an S-curve. The maximum DM accumulation rate of the whole plant was higher than that of the tuber, and appeared 17 days earlier. The distribution of DM in different organs showed two turning points, i.e., during the tuber formation (TF) period and the tuber growth (TG) period. During TF period, the DM accumulation was the greatest in leaf, followed by in tuber. The TF period was also the DM balance period, which occurred 90 days after emergence. Before the DM balance period, the DM accumulation in tuber was lesser than that in root, stem, and leaf, and there was a positive correlation between the DM accumulation in tuber and in root, stem, and leaf. However, after the DM balance period, the DM accumulation in tuber was greater than that in root, stem, and leaf, and the correlation was negative. At seedling stage and in TF period, TG period, starch accumulation period, and maturity period, the DM accumulation in whole plant was 5%, 30%, 60%, 4% , and 1%, while that in tuber was 0,18% , 62 , 18% , and 2%, respectively. In the whole growth period, more than 50% of the DM was formed in TG period. The K concentration was the highest in stem and the lowest in tuber, though the K was mostly concentrated in root before the DM balance period. The K accumulation before the DM balance period was mostly in root, stem, and leaf, with the sequence of stem > leaf > root, but after the DM balance period, the K was mainly allocated in tuber, with >60% of the K accumulated in tuber in maturity period.

[Fungal population structure and its biological effect in rhizosphere soil of continuously cropped potato].

Continuous cropping obstacle is one of the main restriction factors in potato industry. In order to explore the mechanisms of potato's continuous cropping obstacle and to reduce the impact on potato's tuber yield, a field experiment combined with PCR-DGGE molecular fingerprinting was conducted to investigate the fungal population structure and its biological effect in rhizosphere soil of continuously cropped potato. With the increasing year of potato' s continuous cropping, the numbers of visible bands in rhizosphere fungal DGGE profiles increased obviously. As compared with that of CK (rotation cropping), the operational taxonomic unit (OTU) in treatments of one to five years continuous cropping was increased by 38.5%, 38.5%, 30.8%, 46.2%, and 76.9% respectively, indicating that potato's continuous cropping caused an obvious increase in the individual numbers of dominant fungal populations in rhizosphere soil. Also with the increasing year of potato's continuous cropping, the similarity of the fungal population structure among the treatments had a gradual decrease. The sequencing of the fungal DGGE bands showed that with the increasing year of continuous cropping, the numbers of the potato's rhizosphere soil-borne pathogens Fusarium oxysporum and F. solani increased obviously, while the number of Chaetomium globosum, as a biocontrol species, had a marked decrease in the fifth year of continuous cropping. It was suggested that potato' s continuous cropping caused the pathogen fungal populations become the dominant microbial populations in rhizosphere soil, and the rhizosphere micro-ecological environment deteriorated, which in turn affected the root system, making the root vigor and its absorption area reduced, and ultimately, the tuber yield decreased markedly.

[Effects of different film mulch and ridge-furrow cropping patterns on yield formation and water translocation of rainfed potato].

This paper studied the effects of different film mulch and ridge-furrow cropping patterns on the yield formation and water translocation of rainfed potato in the semi-arid area of west Loess Plateau. Comparing with those under traditional harrowed bedding without film mulch (T1), the potato yield under harrowed bedding with film mulching (T2), completely mulched alternating narrow and wide ridges with furrow planting (T3), completely mulched alternating narrow and wide ridges with ridge planting (T4), mulched raised bedding with furrow planting (T5), and mulched raised bedding with bedding planting (T6) was increased by 50.1%, 75.9%, 86.8%, 69.6%, and 60. 6%, and the water use efficiency (WUE) was increased by 47.0%, 82.7%, 84.0%, 75.2%, and 54.3% respectively, with the increments being the highest under T4 and T3. All the film much and ridge-furrow cropping patterns improved the yield component of potato, and T4 and T3 were most beneficial to the increase of mid and big tubers, tuber number per plant, and tuber yield per plant, and to the decrease of the proportions of green and blet tubers. It was concluded that completely mulched alternating narrow and wide ridges with ridge planting (T4) and completely mulched alternating narrow and wide ridges with furrow planting (T3) were the two better cropping patterns in water-saving and high yielding for potato cultivation in semiarid areas.

[Effects of limited supplemental irrigation with catchment rainfall on potato growth in rainfed areas of western Loess Plateau].

Field experiments were conducted to study the effects of limited supplemental irrigation with catchment rainfall on the growth of potato cultivars Daxiyang and Tongshu 23 in rainfed areas of western Loess Plateau. Supplemental irrigation with catchment rainfall at seedling stage increased the potato yield significantly, and the increment was higher for Daxiyang than for Tongshu No. 23. Supplemental irrigation at tuber expanding stage increased the yield of Tongshu 23, but decreased the yield of Daxiyang. Low amount of supplemental irrigation (45 mm) increased the water use efficiency (WUE) and irrigation water use efficiency (IWUE) of Tongshu 23. For Daxiyang, its WUE and IWUE were higher when the supplemental irrigation was made at seedling stage than at tuber expanding stage. Supplemental irrigation increased the tuber yield and the percentages of bigger and medium tubers of Tongshu 23, but the percentages of green and blet tubers were also increased. As for Daxiyang, supplemental irrigation increased the percentages of bigger and smaller tubers, as well as the percentage of blet tuber.