Resistance mechanisms and fitness of pyraclostrobin-resistant isolates of Lasiodiplodia theobromae from mango orchards

Background Stem-end rot, caused by Lasiodiplodia theobromae (Pat.) Griffon & Maubl is a serious postharvest disease in mango. In China, a high prevalence of the QoI fungicides resistance has been reported in the last decade. The study aimed to discuss factors determining rapid development of pyraclostrobin-resistance and its resistance mechanisms. Methods To determine the resistance stability and fitness of pyraclostrobin resistance in L. theobromae, three phenotypes of pyraclostrobin resistance were compared and analyzed for the EC50 values, mycelial growth, virulence and temperature sensitivity and osmotic stress sensitivity. The relative conductivity and enzyme activities of different phenotypes were compared under fungicide stress to explore possible biochemical mechanisms of pyraclostrobin resistance in L. theobromae. The Cytb gene sequences of different phenotypes were analysed. Results All isolates retained their original resistance phenotypes during the 10 subcultures on a fungicide-free PDA, factor of sensitivity change (FSC) was approximately equal to 1. The resistance-pyraclostrobin of the field isolates should be relatively stable. Two pyraclostrobin-resistant phenotypes shared similar mycelial growth, virulence and temperature sensitivity with pyraclostrobin-sensitive phenotype. After treated by pyraclostrobin, the relative conductivity of the sensitive phenotype was significantly increased. The time of Pyr-R and Pyr-HR reached the most conductivity was about 8–10 times than that of Pyr-S, the time for the maximum value appearance showed significant differences between sensitive and resistant phenotypes. The activities of Glutathione S-transferase (GST), catalase (CAT) and peroxidase (POD) of Pyr-HR were 1.78, 5.45 and 1.65 times respectively, significantly higher than that of Pyr-S after treated by 200 mg/l pyraclostrobin. Conclusion The results showed that the pyraclostrobin-resistant phenotypes displayed high fitness and high-risk. The nucleotide sequences were identical among all pyraclostrobin-resistant and -sensitive isolates. The pyraclostrobin resistance was not attributable to Cytb gene alterations, there may be some of other resistance mechanisms. Differential response of enzyme activity and cell membrane permeability were observed in resistant- and sensitive-isolates suggesting a mechanism of metabolic resistance.

Determination of tobacco (Nicotiana tabacum) seed vigour using controlled deterioration followed by a conductivity test

Seeds of eight lots of four tobacco varieties differing in vigour were studied. The initial germination percentage (GPUT) was 81-100% and the controlled greenhouse emergence percentage (CEP) was 55-91%. All seeds were treated by controlled deterioration (CD) at 20% moisture content and 45°C for 24 hours, then some seeds were subjected to a standard germination test and the rest of the seeds were subjected to a conductivity test. The electrical conductivity (EC) of seed soak water was measured every six hours up to 54 hours. The results showed that relative conductivity after CD (RCCD) was highly significantly correlated with GPCD after 30 to 48 hours soaking (r = -0.9324 to -0.9409, P < 0.001). After 36 and 42 hours, RCCD was significantly correlated (P < 0.01) with CEP (correlation coefficients of -0.9120 and -0.9137, respectively). Therefore, it is suggested that measuring relative conductivity after CD could be used to rank tobacco seed lots for vigour. In addition, the best seed soaking time for EC measurement is 36 to 42 hours, with respect to both efficiency and accuracy.

SALICYLIC ACID INDUCES PHYSIOLOGICAL AND BIOCHEMICAL CHANGES IN PEONY UNDER WATERLOGGING STRESS

In this study, the effects of salicylic acid to antioxidative activity and photosynthetic characteristics in waterlogging stress of two peony cultivars (‘Fengdanbai’ and ‘Mingxing’) were investigated. 4-year-old peony grown in different levels of waterlogging stress and then different concentration prepared SA (0.0, 0.1, 0.5 and 1.0 mmol L–1) sprayed on fresh leaves of peony. The antioxidative enzymes activities include superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), chlorophyll content, relative conductivity and MDA content were measured in leaves about different waterlogging treatment, the photosynthetic characteristics were also measured using photosynthetic measurement system. The results showed that waterlogging stress decreased the chlorophyll content in all peony cultivars leaves, but with SA treatment can inhibit the decrease of chlorophyll content. Relative conductivity increased as the extension of waterlogging time in two cultivars. SA treatment could effectively inhibit the increase of relative conductivity, and 0.5 mmol L–1 of SA was the most suitable concentration. SOD, POD, CAT activity increased first and then decreased in different waterlogging condition, SA significantly increased the activity of various enzymes. MDA content was increase as the expansion of waterlogging time in two cultivars. SA inhibits the increase of MDA content. Of all concentration of SA, 0.5 mmol L–1 was the best concentration to inhibit the waterlogging stress. For the photosynthetic characteristics, the net assimilation rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and intercellular CO2 (Ci) were decreased under different waterlogging condition. SA treatment can increase Pn, Gs, Tr and Ci of peony.

Effects of Chitosan on Soluble Sugar Content in Prunus davidiana Seedlings

A pot experiment was conducted to study the effects of different concentrations of chitosan solutions (0, 1, 2, 4, 6 g/L) on soluble sugar content in Prunus davidiana seedlings. The result showed that there was no significant difference of the soluble sugar content in roots, stems, leaves and shoot in P. davidiana seedlings between at 1 g/L concentration and the control. All concentration treatments were reduced the soluble sugar content in roots and stems of P. davidiana seedlings compared with the control. On the contrary, all concentration treatments were improved the soluble sugar content in leaves and shoot of P. davidiana seedlings compared with the control and the concentration treatment of 2 g/L and 4 g/L was at a higher level. All concentration treatments were improved the content in relative conductivity of blade in P. davidiana seedlings and the concentration treatment of 4 g/L was at a higher level. On the contrary, all concentration treatments were reduced the content in soil conductivity. Therefore, the chitosan solutions concentration of 2 g/L and 4 g/L concentration was beneficial to soluble sugar content in P. davidiana seedlings. On the contrary, high concentration of chitosan solutions was not good for soluble sugar content.

Effects of Different Compound Treatments on Cold Resistance of Pitaya Plants

In this study, using red pulp pitaya plants variety ’Taiwan No. 6’ as experiment material, 2, 4-epitheloside (BR), betaine (GB), calcium chloride (CaCl2) and salicylic acid (SA) were selected as experimental factors which were set at three levels. The effects of different treatments on the cell membrane stability and osmotic adjustment substances of pitaya plants were studied by orthogonal design. The results showed that salicylic acid was the main factor affecting the relative conductivity and soluble sugar content. 2, 4-epibrassinolide was the main factor affecting the content of malondialdehyde and free proline. CaCl2 was the main factor affecting the soluble protein content. The best concentration combination for improving the cold resistance of pitaya plants was as follows: BR 1 μg/L, GB 2.5 mmol/L, CaCl2 250 mg/L, and GA 0.5 mmol/L.

Identification of Manganese Distribution Using Very Low Frequency (VLF) Method at Karangsari Village, Pengasih Sub-District, Kulonprogo Regency, DIY

Research of manganese distribution was conducted in the village of Karangsari, Pengasih sub-district, Kulonprogo Regency, DIY which is the former area exploration and exploitation of manganese. The purpose of the research is known the value of relative conductivity and the distribution of manganese. The method used very low frequency tilt mode. The tools used 2 set of T-VLF BRGM (sensor and monitor) and the data processing software are Ms. Excel and KHFILT. T-VLF operated with 2 frequencies that are 19800 Hz from Australia and 22.200 Hz from Elbino Japan. The total lines are 6 lines with 75 m space. Distance between measured points is 15 m, whereas line length is 300 m. The parameters measured from VLF method are tilt (%) and ellipticity (%). The raw data VLF is processed by Ms Excel to obtain a tilt, ellipse, fraser graph vs distance and the RAE from Karous Hjelt filter. While the results of processed by KHFILT software is the equivalent current density contour map. Relative conductivity of area research are line 1 (-10 to 10) mho/m, line 2 (-40 to 30) mho/m, line 3 (-20 to 20) mho/m, line 4 (-30 to 10) mho/m, line 5 (-40 to 30) mho/m and line 6 (-30 to 40) mho/m. The spread of manganese were in the high conductivity, toward west and east of research area with depth up to 45 m.

Effects of Drought Stress on Physiological Properties of Gazania rigens L.

Under artificial drought environment, membrane permeability, malondialdehyde (MDA) content and free proline (Pro) content of three cultivars of gazania were studied as well as the relation between the three physiological indexes and drought resistance. The results showed that: there existed significant positive correlation between relative conductivity and drought resistance in ‘Hongwen’; while ‘Xingbai’ and ‘XH’ showed the reverse result. The correlation between Pro content and drought stress treatment days in the three cultivars were significant positive. However, the correlation between MDA content and drought stress treatment days in the three cultivars were not the same. Therefore, Pro content can be chose as a physiological indicator to evaluate drought resistance in gazania.

Evaluation of Cold Resistance of Hosta Species in Harbin City

Hosta undulate, Hosta plantaginea and Hosta plantaginea ‘Rosea’ were introduced to Harbin to evaluate the cold resistance compared to Hosta ventricosa stearn which can survive during the winter in Harbin. The physiology characteristics of Hosta species were determined under ground conditions. Along with the temperature drop, the increase of relative conductivity and MDA content of Hosta undulate were lower than Hosta plantaginea and Hosta plantaginea ‘Rosea’. Whereas contents of soluble sugar and free praline of Hosta undulate were higher than these two Hosta species. In view of the minimum temperature of winter in Harbin, chilling tolerance were conducted at -35°C and -40°C for 3h, 6h and 9h. Hosta undulate shows outstanding cold resistance and recovery growth.