فصلنامه گیاه پزشکی
سال چهل و دوم شماره 4 (زمستان 1398)

Background and Objectives:

 Water pH is one of the most important factors that affects the inefficiency of insecticides against the common pistachio psyllid, Agonoscena pistaciae Burckardt and Lauterer (Hemiptera: Aphalaridae), as the most important pest in Iran's pistachio orchards.

 Materials and Methods:

 In this study, the effect of insecticides including spirotetramat (Monvento® SC 10%) and imidacloprid (Confidor® SC 35%) and pH reducing agents, such as Rectiphier® and Citral pH®, on the reduction of population density of eggs and nymphs of common pistachio psyllid were investigated under field conditions. The experiment was carried out as randomized complete block design with four replications. The samplings were done one day before and 3, 7, 14, 21 and 28 days after spraying.

 Results:

 The results indicated that adding Rectiphier and Citral pH to the insecticides had no significant effect on increasing the efficacy of spirotetramat and imidacloprid on eggs population of pistachio psyllid, and only on 7 days after spraying, adding of Rectiphier to imidacloprid significantly increased the efficiency of the insecticide, and reduced the amount of oviposition of A. pistaciae (91.58%). The results of the effect of different treatments on nymphs population density of A. pistaciae showed that the effect of insecticides + pH reducing agents was more than application of insecticides alone, but their effect was not significant, and only on 3 and 7 days after spraying, Rectiphier significantly increased the effect of imidacloprid. The reduction of nymphal population densities in imidacloprid + Rectiphier treatment were 90.13% and 93.23%, on those sampling dates, respectively. 

Discussion:

PH reducers (Rectifier and Citral pH) could have the potential to increase the efficacy of spirotetramate and imidacloprid or other insecticides to control A. pistaciae and produce healthy crops, reduce costs, environmental hazards and side-effects on natural enemies and to minimize application of chemical insecticides. However, more research is needed with regard to the effect of different compounds of pH reducer, different concentrations of those compounds and also the effect of these compounds on different water pH. 

Quorum sensing (QS) is a process of cell to cell communication that allows bacteria to be aware about cell density. In this phenomenon bacteria communicate with each other through signaling molecules such as N-acylhomoserine lactones (AHLs). Also, virulence gene expression in many pathogenic bacteria like Pectobacterium is under control of QS. Some bacteria can degrade AHLs molecules by a process called anti quorum sensing or quorum quenching (QQ); therefore, QQ can be used in biocontrol of plant pathogenic bacteria. The main purpose of this research was to detect QQ genes in strong QQ-based biocontrol bacteria.

In this investigation, QQ bacteria were isolated from rhizosphere and phyllosphere of some agricultural and non-agricultural plants using minimum media containing AHL. QQ bacteria were identified using biosensors CV026 and VIR07. Mechanism of QQ action was determined by heating, proteinase treatment and filtering methods. Afterwards, in order to find acylase and lactonase genes in these bacteria, homology searches were performed using BLASTn and BLASTp in NCBI. Then, several primers were designed by several softwares including CLC main workbench 5.5, Primer Premier 6, Primer3, Oligo7 and primer BLAST.

The most abundant and strongest QQ isolates were shown enzymatic activity. Main twenty-seven isolates with high QQ activity were detected. Four genera and species including Pseudomonas chlororaphis, Pseudomonas putida, Acinetobacter sp. and Bacillus sp. were found as the bacteria with highest QQ and biocontrol ability against Pectobacterium. As a results of this study, in the Bacillus Aiia lactonase gene;in P. chlororaphis three acylase genes of pvdQ، quiP and hacB; in P.putida two acylase genes of  pvdQ and quiP  and in Acinetobacter one acylase genes were traced.

According to the results of this investigation, Pseudomonas genus was determined as the frequent QQ bacteria. Also, P. chlororaphis species with the strongest QQ activity, were divided in to two groups; the first isolates with two acylase genes (pvdQ and quiP) and the second isolates containing extra homologous acylase hacB. Isolates of the latter group with the most detected genes involved in QQ, were identified as the best QQ-based biocontrol bacteria against Pectobacterium.

Background and Objectives:

 Khuzestan is the only province with sugarcane cultivation. One of the limiting factors in the production of this crop is the occurrence of frost damages in some years. Since no comprehensive research has yet been conducted on detection and evaluation of bacteria with the potential to form nuclear ice in frostbite, this study was carried out to evaluate this subject.

 Materials and Methods:

 This study was carried out in the laboratory of Institute for Research and Training of Sugar and Auxiliary Industries. Endophytic and epiphytic strains of bacteria were isolated from sugarcane. To test the freezing potential of representative strains, four tests including, "determination of Ice nucleation activity by freezing in the tube", "freezing droplet test at -20 °C", "Ice nucleation test on sugarcane cut leaves in vitro" and "Ice nucleation test on sugarcane plant in greenhouse conditions" were performed. Also the genes of the nucleus were detected by 3076f / 3463r and 3308f / 3463r specific primers. 

Results:

 Results show that bacteria species B. gladioli, B. fungorum, B. cantaminans, M. huakuii, O. ciceri, M. proteolyticum, M. Foliorum, R. solanacearum , R. picketii and X. campestris had different degrees of symptoms. In addition, the genes of the nucleus were detected by 3076f / 3463r and 3308f / 3463r specific primers. For all of above mentioned bacterial strains, specifically strain X. campestris, no references have been reported of ice nucleation activity. To assess susceptibility or resistance of sugarcane, cultivar CP69-1062 were the most susceptible and highly damaged in the tests including "Ice nucleation test on sugarcane cut leaves in vitro" and "Ice nucleation test on sugarcane plant in greenhouse conditions". In addition, CP57-614 and CP48-103 cultivars showed minimum variation in frosting in compression to CP69-1062 cultivar. Two cultivars including CP73-21 and SP70-1143 exhibited a high degree of resistance to frostbite.

 Discussion:

 Due to the high variation among Ice-Nucleating bacteria and the sensitivity of commercial cultivars, our finding can be a suitable option for producers and encourage them to use resistant cultivars in the field.

Background and Objectives:

 Life table parameters are important and key tools to reveal the reproductive and population growth potential of natural enemies regarding control of their prey/host. 

Materials and Methods:

 The initial population of Cephalonomia tarsalis was collected from wheat storage facilities in Tehran province. Life table parameters of C. tarsalis on the 3th instar larvae of Oyzaephilus surinamensis were investigated using100 newly laid eggs (as a cohort) at temperature of 25±1 °C, 60±5% R.H. and photoperiod of 16:8 (L:D) hours. The daily counts of mortality and fecundity were arranged as a life table and used to calculate net reproductive rate (Ro), intrinsic rate of increase (rm), finite rate of increase (λ), mean generation time (T) and doubling time (DT).

 Results:

 As a result of this study survival rate (lx) decreased with increasing age and life expectancy (ex) at birth 43/8 days. Egg hatch rate (hx) was determined to be 0.96. As a result of this study, the gross fecundity and fertility rates were determined to be 84.74±0.61 and 81.35±0.58 and net fecundity and fertility rates were 60.9±2.03 and 58.46±1.95, respectively. The average number of eggs produced per female per day was 2.56±0.01. The intrinsic rate and finite rate of C. tarsalis on the 3th instar O. surinamensis were 0.104±0.001 and 1.11±0.001 day-1 , respectively. Time required to increase the population to the size of the net reproduction rate and doubling times were 36.2±0.065 and 6.62±0.059 days, respectively. The gross and net reproduction rate were 61.37±0.159 egg and 44.1±1.47 females/females/generation, respectively. The results of this study on the stable age distribution showed that 91.14 % and 8.02 % of the population belonged to immature stage and adults, respectively.

 Discussion:

Based on the findings, it could be concluded that C. tarsalis has a good potential to control its host, C. tarsalis.

Background and Objectives:

 The genus Fusarium has a worldwide distribution and many of its species, especially Fusarium graminearum Schwabe and Fusarium culmorum (W.G. Smith) Saccardo can infect a wide range of host plants and cause a variety of economically important diseases. The aim of this study was to identify the constituents of essential oil from leaves of native neem tree (Azadirachta indica A.Juss.) and their effect on growth performance and activity of cell wall degrading enzymes produced by these pathogens. 

Materials and Methods:

 The leaves of neem tree were obtained from Iranshahr region of Sistan and Baluchestan province and dried in the shade. The essential oil was extracted by hydrodistillation using a clevenger apparatus and its major constituents were identified by gas chromatographymass spectrometry. 

Results:

 The major constituents in the essential oil were β-elemene (27.2%), caryophyllene (15.9%) and phytol (15.3%), which have antifungal effects against F. graminearum and F. culmorum. The results showed that although the pathogenicity of F. culmorum was lower than F. graminearum, but the minimum inhibitory concentration of essential oil, βelemene, caryophyllene and phytol against F. graminearum was higher than F. culmorum. Sporulation and spores germination of Fusarium spp. were completely inhibited by essential oil and phytol. Synergistic effects of the main constituents of essential oil showed that combining phytol with caryophyllene induced a synergistic activity against Fusarium spp. and in combination with β-elemene caused an additive effect. Activities of cellulase and pectinase, as main cell wall degrading enzymes were decreased by essential oil and its main constituents at low concentration without affecting mycelial growth of fungi studied. 

Discussion:

 The findings of this research showed that there is a possibility of using neem oil and phytol compound to control diseases caused by Fusarium species.

Background and Objectives:

 The melon aphid, Aphis gossypii Glover, is one of the most important pests of tomato in Iran. This aphid causes severe damage on tomato crop in northern Iran. 

Materials and Methods:

 Present study was conducted in an experimental field, 0.3 h, in Behshahr region in Mazandaran province based on a randomized completely block design. In this study, the effectiveness of intercropping tomato (T) with clover (C) in the three combinations: (1) one row of tomato with two rows of clover (1T:2C), (2) two rows of tomato with two rows of clover (2T:2C), and (3) three rows of tomato with two rows of clover (3T:2C) along with sole tomato were assessed on the densities of melon aphid, Aphis gossypii Glover, diversity of its natural enemies and yield of both crops in 2016 and 2017.

 Results:

 The density of nymphs and adults of A. gossypii were significantly higher in sole tomato compared with intercrops. Among intercrops, the lowest density of nymphs and adults of A. gossypii were observed in 1T:2C intercrop. In present study, 13 predator species were collected and identified on aphid-infested plants of tomato in the experimental field. Among the predators, Coccinella septempunctata L., Chrysoperla carnea (Stephens) and Episyrphus balteatus DeGeer had more abundance in the two studied years.  The Shannon diversity index (H´) and the Pielou’s evenness index (J´) for composition of predator species were significantly higher in intercrops compared with sole tomato crop. Moreover, more nymphs and adults of A. gossypii were parasitized in all intercrops compared with sole tomato crop in 2016 and 2017. The highest value of land equivalent ratio was found in 1T: 2C (LER = 1.28 in 2016 and 1.30 in 2017) among intercrops in the two cropping seasons.   

Discussion:

 All the three intercropping patterns of tomato with clover including 1T:2C, 2T:2C and 3T:2C, especially 1T:2C could be recommended in management programs of the melon aphid in tomato fields.