Efficacy and timing of application of fungicides for control of citrus postbloom fruit drop

Citrus postbloom fruit drop (PFD) caused by Colletotrichum spp. occurs in several countries in the Americas reducing yields by as much as 80%. Fungicide application is the main strategy for PFD control. Two field trials were performed to assess the timing of applications and another two were set up to investigate the efficacy of fungicides for PFD control in São Paulo State, Brazil. The percentage of symptomatic flowers per branch, the number of persistent calyces per branch, the number of fruit per branch and yield were evaluated. Four sprays of trifloxystrobin + tebuconazole, carbendazim, difenoconazole or cyprodinil + fludioxonil were effective in reducing yield losses due to PFD, however the trifloxystrobin + tebuconazole mixture was significantly more effective than all other treatments. The conventional PFD control programme, with one spray of difenoconazole followed by up to three carbendazim applications at different intervals, showed variable results, probably due to rainfall. The trifloxystrobin + tebuconazole mixture was effective at controlling PFD under favourable conditions for infection and can be recommended in PFD control programmes.     

Repellency of selected Psidium guajava cultivars to the Asian citrus psyllid,Diaphorina citri

Huanglongbing (HLB) is the most devastating disease of citrus worldwide. It is caused by bacteria of the genus ‘Candidatus Liberibacter’ and transmitted by two psyllid species, the Asian citrus psyllid (ACP) Diaphorina citri, and the African citrus psyllid Trioza erytreae. Considerable research has been conducted toward developing and implementing HLB and ACP management strategies. With respect to ACP control, of interest is that reports indicate guava, Psidium guajava, can be repellent to ACP. We conducted research to further evaluate repellency of guava to ACP. In one set of experiments, guava oil from five Brazilian guava cultivars (‘J3’, ‘Pedro Sato’, ‘Século XXI’, ‘Thailand’ and ‘Paluma’) was extracted from leaves (immature and mature) by hydro-distillation in a Clevenger-type apparatus and evaluated for psyllid repellency. In a second set of experiments, repellency of guava leaves to ACP was investigated using leaves (immature and mature) from two guava cultivars in Florida, ‘Pink’ and ‘Thai White’. In each set of experiments, repellency was evaluated by releasing ACP adults into a cage with two large vials, one containing a young flush shoot (= immature leaves) of Murraya exotica (a favored host plant of the psyllid, the flush of which is highly attractive to ACP) and one with M. exotica flush and the test material of interest (guava oil, immature guava leaf or mature guava leaf). The adults were free to move throughout the cage and into the vials, and the number of psyllids in each vial was counted after 24 h. The results showed that all guava materials tested had at least some repellency to ACP. Mature leaves tended to have a greater repellent effect than immature leaves. Each of the five oils exhibited repellency. A report in the literature suggested that sulfur compounds associated with guava may be responsible for ACP repellency. Interestingly, the five guava oil extracts we studied were repellent to ACP but none contained any sulfur compounds. Identification of the constituents responsible for repellency could lead to new ACP management tactics.     

Effects of kaolin-based particle film to control Ceratitis capitata (Diptera: Tephritidae) infestations and postharvest decay in citrus and stone fruit

Ceratitis capitata (Wiedemann) is a major pest of fruit crops due to its wide host range and distribution. The objectives of this study were to evaluate the effectiveness of Surround WP, a kaolin-based particle film, as an alternative to synthetic insecticides to control medfly infestations and postharvest decay in citrus and stone fruit. No-choice, choice and half-choice laboratory experiments with citrus fruit, nectarines and peaches showed a significant reduction of medfly punctures and landings on kaolin-treated fruit. The total loss at harvest in satsumas sprayed with Surround WP (17%) was significantly lower than in those untreated (57%) or treated with trichlorfon (68%). In 2004, the yield loss at harvest in peaches and nectarines treated with Surround WP was not different compared to fruit sprayed with fenthion and trichlorfon, while in 2005 Surround WP was significantly more effective than insecticides in reducing the incidence of damaged fruit. Citrus and stone fruit treated with Surround WP showed a lower incidence of postharvest decay than control and insecticide-treated fruit. The present study shows for the first time the lower incidence of postharvest decay in fruit protected with Surround WP, which represents a suitable alternative to conventional insecticides in integrated and traditionally managed orchards.     

Enhancement of biocontrol efficacy of Pichia membranaefaciens by hot water treatment in postharvest diseases of citrus fruit

Effects of hot water treatment (HWT; 53 °C for 2 min) and Pichia membranaefaciens, either alone or in combination, on controlling Penicillium italicum, Penicillium digitatum, and natural infection in citrus fruit were investigated. Results showed that the combined treatment significantly reduced disease incidence and lesion diameters of blue and green molds in artificially inoculated fruit whether the pathogens were inoculated after or before the treatment compared with the treatment of P. membranaefaciens or HWT alone. The combination of P. membranaefaciens with HWT was as effective as the fungicide treatment in natural infection trials. Application of HWT did not affect the growth of P. membranaefaciens in the wounds of citrus fruit at 20 °C or 4 °C. P. membranaefaciens combined with HWT effectively enhanced the phenylalanine ammonia-lyase, peroxidase, polyphenoloxidase, chitinase, and β-1,3-glucanase activities and stimulated the synthesis of phenolic compounds. These results suggest that the use of HWT is a useful approach to improve the efficacy of P. membranaefaciens in postharvest diseases of citrus fruit.     

Screening of the susceptibility of newly released genotypes of potato to thrips infestation under field conditions in northwest Iran

Use of host plant resistance is an essential component of integrated management of Thrips tabaci Lindeman. The present research was designed to screen five commercial cultivars of potato, namely Agria, Kondor, Morene, Diamant and Savalan, and two breeding lines 397082-2 and Khavaran for their susceptibility to thrips infestation and for their mean relative plant growth rate (MRGR) and crop yield in an experimental field (not frected with insecticides) and a control field (chlorpyrifos frected) in the Ardabil region of Iran in 2011 and 2012. Thrips populations were assessed by visual inspection on potato leaves. At harvest time, the percentage of leaf area damaged by thrips infestation was assessed on leaves of the tested genotypes. All adults of phytophagous thrips collected in the experimental field were T. tabaci. In both years the mean numbers of thrips adults and larvae were lowest on Savalan cultivar among the tested genotypes. The mean damage index was also lowest on Savalan in both years and the MRGR and the mean yield were greatest in Savalan in the control field. Moreover, in thrips-infested plants, the lowest percentage of MRGR loss and the lowest percentage of yield reduction were observed in Savalan (3.7% and 5.8%, respectively). Of the genotypes tested, Savalan is the most resistant host and has potential for use in the sustainable management of T. tabaci on potato.     

Optimization of germination conditions to enhance hydroxyl radical inhibition by water-soluble protein from stress millet

This study aimed to further increase the yield of the hydroxyl radical inhibitory water-soluble protein from stress germinated millet. For this, the effects of the sprouting conditions (temperature, time and pH of stress medium) on the hydroxyl radical inhibition were investigated carefully by single-factor experiments and statistical experimental designs, which included a fractional factorial design, steepest ascent experiments, a central composite experimental design and response surface methodology. The optimal conditions were identified as temperature 28 °C, culture time 54 h and stress medium pH 7.5. Under the optimum conditions, the highest inhibition (60.38%) was achieved.     

Suppression of green peach aphid (Myzus persicae) (Sulz.), citrus mealybug (Planococcus citri) (Risso), and two spotted spider mite (Tetranychus urticae) (Koch.) attacks on tomatoes and cucumbers by aqueous extracts from vermicomposts

Vermicomposts are produced through interactions between earthworms and microorganisms in the breakdown of organic wastes. Aqueous extracts were prepared in commercial brewing equipment (Growing Solutions Inc.) from vermicomposts processed from pre-consumer food waste. The ratio of vermicompost to water was 1 to 5 v:v to produce a 20% aqueous solution. The effects of soil drenches at dilutions of 20%, 10%, and 5% vermicompost extracts, were compared with those of deionized water, in the suppression of green peach aphids, mealybugs, and two spotted spider mites attacking tomatoes and cucumbers, in greenhouse cage experiments.     

A novel concept for the control of parasitic weeds by decomposing germination stimulants prior to action

A new concept for controlling parasitic weeds is described. By decomposing germination stimulants prior to action no germination of seeds can take place anymore. Ethanol fractions of the strigolactone (SL) analogues viz., the standard synthetic analogues GR 24 and Nijmegen-1, and analogues derived from tetralone and coumarine, were added to an aqueous buffer with a pH ranging from 6 to 8 and the half lifes (t_1/2) of the hydrolysis were measured. Nijmegen-1 hydrolysed faster than GR 24 and the analogue from tetralone was the most stable one at all pH's. It was found that the aqueous solutions of either borax or thiourea rapidly decompose typical SL analogues, including GR 24 and Nijmegen-1, within an hour. The hydrolysis of SLs by borax was monitored with UV spectroscopy and for thiourea gas chromatography was used. This decomposition of SLs by either borax or thiourea in natural conditions would deprive the seeds of the parasitic weeds of the essential germination stimulants and as a consequence not allow them to germinate. Hence, conditions for an effective weed control are fulfilled.     

Synergism between potassium sorbate dips and brief exposure to high CO2 or O2 at curing temperature for the control of citrus postharvest green and blue molds

Synergistic effects and very effective control of citrus postharvest green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively, were observed on artificially inoculated ‘Valencia’ oranges and ‘Clemenules’ and ‘Ortanique’ mandarins after a potassium sorbate (PS) treatment was followed by 2 days of storage in atmospheres of elevated CO₂ or O₂ at a curing temperature. A combined treatment consisting of 60-s dips in aqueous solutions of 3% PS heated to 62 °C was followed by 48-h exposure to air, 15 kPa CO₂ or 30 kPa O₂ at 33 °C. Control treatment was a 60-s water dip at 20 °C followed by 24-h exposure to air at 20 °C. Synergism was observed on citrus fruit either incubated at 20 °C for up to 22 days, simulating direct commercialization, or stored at 5 °C for up to 45 days, simulating commercial cold storage. This research offers potential new tools to the citrus industry for implementation of nonpolluting integrated postharvest disease management programs, especially devoted to high added value organic markets or export markets with zero residue tolerance.     

Rate of spread of PVYn by alateMyzus persicae (Sulzer) from infected to healthy plants under laboratory conditions

Summary Alate green peach aphids,Myzus persicae (Sulzer), tested in a flight chamber during their maiden flight period displayed behaviours ranging from repeated trivial flights to settling on the plants. The interaction of alate vector density and PVYⁿ spread was dichotomous, virus spread was significantly related to vector density in some trials but virus spread was nil or limited and not significantly dependent on vector density in others. The green peach aphid colony used in these experiments provided a mixture of active and highly active alate populations. Results suggest that inactive and active vectors came from the active and highly active alate populations, respectively. Therefore, winged aphids within a species cannot all be attributed the same vector efficiency unless known to originate from the same population. At a 15% inoculum level the intercept for the regression model for the spread of PVYⁿ was 5.03% indicating that there is a significant probability of propagation at aphid densities as low as one. However, over the range of aphid densities tested, the rate of spread per aphid was low, 0.08%, suggesting that reinfection of newly infected plants or movement interference between aphid vectors rapidly became important factors negatively affecting virus spread. Although these results cannot be directly transferred to field conditions they provide confirmation that lowM. persicae numbers can transmit unacceptable levels of mosaic and that low inoculum levels are required to decrease the risk of transmission by the small aphid numbers which cannot be realistically controlled.     

培养条件对平贝母愈伤组织生长和生物碱积累的影响研究

目的 了解培养条件对平贝母愈伤组织生长和总生物碱含量的影响.方法 分别以光暗培养、氮源比例、碳源种类、蔗糖浓度、磷酸盐浓度作为影响因子进行愈伤组织培养.结果 光培养条件、NH4＋∶NO3-=1∶1、蔗糖4％、磷酸盐浓度1.5mmol· L-1时,平贝母愈伤组织生长较快、总生物碱积累较多,结论 培养条件对平贝母愈伤组织生长和总生物碱积累均有影响.     

用水稻苗期叶绿素含量相对稳定期估算水稻剑叶光合功能期的方法研究

 用SPAD-502型叶绿素计测定了8个水稻品种不同叶位连体与离体叶片叶绿素含量的变化，结果表明叶片全展后（或离体后）叶绿素含量变化可明显划分为相对稳定期和速降期两个阶段。离体与连体叶片、不同叶位叶片间的叶绿素含量相对稳定期均呈极显著线性回归关系。进一步测定其他34个品种幼苗期离体第6叶和连体剑叶叶绿素含量相对稳定期并进行若干方程曲线拟合表明，用多项式表示两者之间关系的相关系数最大（r＝0.9619,P< 0.01）。用该拟合方程对另外10个品种剑叶的光合功能期估算并与实测值之间进行相关分析表明，估算值与叶绿素含量相对稳定期和光合速率高值持续期的实测值均达极显著水平，其相关系数分别为0.9948和0.9913(P < 0.01)。进一步证实了上述关系的存在。     

Soak conditions and temperature following sowing influence the response of maize (Zea mays L.) seeds to on-farm priming (pre-sowing seed soak)

On-farm seed priming of maize (i.e. soaking seed in water overnight, 17 h) in the semi-arid tropics has been shown to improve crop establishment and yield but the benefits can be variable. In previous work, this variation was thought to result from the interaction between primed seeds and conditions in the seedbed following sowing. To investigate this interaction, experiments were carried out under controlled temperature conditions that represented those of seedbeds in the semi-arid tropics. The conditions during seed priming and during subsequent germination and emergence were investigated as potential causes of variable seedling emergence relative to that of untreated seeds. Priming advanced emergence from moist sand cores at 30 °C/20 °C (day/night), reduced emergence at 35 °C/28 °C and delayed and reduced emergence at 40 °C/28 °C. In drier cores (drained 8 days) at 35 °C/28 °C, priming advanced germination time and did not decrease final percentage emergence. These results confirmed earlier field observations that the effect of priming in maize can vary and lead to positive, neutral or negative effects. Priming decreased the optimum and ceiling temperatures for germination, and unlike untreated seeds, the relationship between germination rate and sub-optimal temperature was not linear in all cases. Pre-humidifying seeds did not enhance the effect of priming, but aerating the soak water did. These results indicate that variable results from priming recorded in the field were not due to imbibitional damage, but may result from the negative effects of hypoxia during soaking exacerbated by moist conditions and high temperatures at sowing. These effects differed between seedlots of different cultivars, indicating the importance of selecting more tolerant maize hybrids to reduce variation in response to priming following sowing in the field. The implications of these findings for the use of primed seeds in the field are discussed.     

Germination responses of the halophyte Chloris virgata to temperature and reduced water potential caused by salinity,alkalinity and drought stress

Chloris virgata is considered a useful grass species for grassland restoration in northern China. However, little information exists concerning the germination responses of this species to temperature and water potential caused by stress conditions. Experiments were conducted in growth chambers to assess the effect of temperature, salinity, alkalinity, drought and the interactions of temperature and stress on seed germination. Seeds were germinated at three diurnal temperature regimes, with four water potentials in NaCl, NaHCO₃ and PEG solutions. Results showed that optimal germination under stress occurred at 15–25 °C, and germination percentages and rates were inhibited by either an increase or decrease in temperature from the optimal temperature. The inhibitory effects of the low water potential caused by salinity and drought on germination were greater at 25–35 °C, but seeds were subjected to more stress despite the relatively higher water potential because of the alkalinity at this temperature. The recovery percentage under salinity was highest at ?1·2 MPa at 15–25 °C, and more than 80% of seeds also germinated at this water potential after they were transferred from drought stress. However, seeds lost their viability in higher alkalinities under all temperatures, and at 25–35 °C, there was lower recovery percentage under stress. Results suggest that salinity, alkalinity and drought stress have different impacts on seed germination, and the tolerance to stress of C. virgata seeds is affected by the interactions of temperature and water potential caused by salinity, alkalinity and drought. Chloris virgata shows potential utility as a promising grass species in salinity–alkalinity and drought‐stressed environments.     

2001～2012年国审玉米品种亲本自交系系谱来源分析

搜集和整理2001～2012年国审普通玉米杂交种及其双亲自交系的来源,分析并绘制亲本自交系的系谱图,根据亲本自交系所属的杂种优势群,分析杂种优势模式的类型与比例.结果表明,属于塘四平头群的亲本自交系主要是黄早四的衍生系,骨干黄改系吉853、LX9801与昌7-2仍然被广泛应用,并且产生多个衍生系被大量应用;旅大红骨群的亲本自交系主要是丹340及其衍生系,其中自交系丹598的多个衍生系成为国审玉米杂交种的亲本自交系;Reid群的亲本自交系数量最大,478衍生系数量达30多个,7922衍生系数量达20多个,5003的衍生系数量为10个以上;PB群的亲本自交系是78599直接选系及其衍生系,其中齐319已产生多个衍生系;Lancaster群的亲本自交系主要是Mo17的改良系.杂种优势模式类型中Reid×塘四平头杂交种所占的比例最大.     

东北三省大豆种质资源对大豆疫霉根腐病的抗性表现

以大豆疫霉根腐病病原菌1、25号生理小种，对黑龙江、吉林、辽宁省的大豆品种（系）956份进行了抗源筛选，筛选出了23个品种（系）兼抗25号和1号生理小种，占供试材料的2．54％。筛选出抗25号生理小种的品种（系）68份，占7．48％，抗1号生理小种的品种（系）251份，占27．77％。     

基于1999—2019年国家自然科学基金资助信息分析茶学基础研究现状

对茶学领域1999—2019年获得国家自然科学基金资助的项目,从项目年度、类别、学部、依托单位性质及其所在区域、项目负责人和学科分支分布等方面进行统计分析,挖掘我国茶学学科基础研究的现状、特点和发展趋势,探讨茶学基础研究中存在的问题和不足,为茶学领域科研人员的选题思路、科研发展提供参考。     

2001～2012 年国审玉米品种数量及骨干自交系的应用分析

搜集和整理2001～2012年国审普通玉米杂交种及其双亲来源,研究每年国审玉米品种数量的变化趋势,对选育的杂交种在2个以上的亲本自交系进行统计,并分析这些自交系的来源。结果发现,普通玉米杂交种2006年审定的数量最多,2003年其次,2007年以后普通玉米杂交种的审定数量在10～20个。在对2001～2012年间国审玉米杂交种亲本来源的分析发现,共有39个亲本自交系组配2个及其以上杂交种,组配杂交种比较多的自交系依次为吉853>丹598>lx9801>昌7-2>京2416>丹340。     

响应面法优化超声波辅助乙醇提取余甘多酚的工艺研究

以提高余甘果肉中的多酚提取率为目的,采用超声波辅助乙醇提取。以乙醇浓度80%为固定条件,通过4组单因素试验探讨了超声波提取温度、功率、提取时间及料液比对余甘多酚提取效果的影响;运用Box-Behnken设计,通过3因素3水平的响应面分析法优化了超声波辅助乙醇提取余甘多酚的工艺。结果表明：在乙醇浓度80％,料液比1 g ∶ 25 mL条件下,余甘多酚的最佳超声波辅助乙醇提取的工艺条件为超声波提取温度43.80 ℃,功率250.96 W,提取时间23.90 min。按此工艺条件提取的余甘多酚提取率为17.21％。     

High level of resistance to Sclerotinia sclerotiorum in introgression lines derived from hybridization between wild crucifers and the crop Brassica species B. napus and B. juncea

Sclerotinia rot caused by the fungus Sclerotinia sclerotiorum is one of the most serious and damaging diseases of oilseed rape and there is keen worldwide interest to identify Brassica genotypes with resistance to this pathogen. Complete resistance against this pathogen has not been reported in the field, with only partial resistance being observed in some Brassica genotypes. Introgression lines were developed following hybridization of three wild crucifers (viz. Erucastrum cardaminoides, Diplotaxis tenuisiliqua and E. abyssinicum) with B. napus or B. juncea. Their resistance responses were characterized by using a stem inoculation test. Seed of 54 lines of B. napus and B. juncea obtained from Australia, India and China through an Australian Centre for International Agricultural Research (ACIAR) collaboration programme were used as susceptible check comparisons. Introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum had much higher levels (P < 0.001) of resistance compared with the ACIAR germplasm. Median values of stem lesion length of introgression lines derived from the wild species were 1.2, 1.7 and 2.0 cm, respectively, as compared with the ACIAR germplasm where the median value for stem lesion length was 8.7 cm. This is the first report of high levels of resistance against S. sclerotiorum in introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum. The novel sources of resistance identified in this study are a highly valuable resource that can be used in oilseed Brassica breeding programmes to enhance resistance in future B. napus and B. juncea cultivars against Sclerotinia stem rot.