Escherichia coli carrying single pectate lyase genes from the phytopathogenicErwinia Chrysanthemi causes disease symptoms in potato

Introduction of the clonedErwinia chrysanthemi pelB orpelE genes intoEscherichia coli enabled the latter to cause blackleg disease symptoms in potato similar to those observed with the pathogenErwinia carotovora. TheE. coli cells multiplied in the roots and moved systemically in the potato stems, concomitant with the appearance of disease symptoms.E. coli cells expressing the clonedpel genes also interacted with the fungal pathogen,Verticillium dahliae, as observed previously withErwinia spp. The results indicate that either of two clonedpel genes permitsE. coli to cause relatively sophisticated diseases in potato plantlets.     

Control of potato powdery scab caused by Spongospora subterranea by foliage cover and soil application of chemicals under field conditions with naturally infested soil

Powdery scab (PS), caused by Spongospora subterranea, reduces the quality and marketability of potatoes worldwide. Disease symptoms include lesions on the tuber surface and root galling, which may lead to yield losses. In the current study we report a sustainable approach to reduce PS by manipulating soil temperature during tuber initiation. Plant cover with nonwoven fabric significantly reduced PS on tubers by 54%–69% in 2017 and 84%–93% in 2019, compared to the control, and root galling by 96% in 2019, due to an increased average minimum and maximum soil temperature of 1.8 and 4.2 °C in respective years. Additional preplanting soil treatments were also evaluated in naturally infested soil. In 2017, disease incidence and severity were significantly reduced using 2.5 or 5 L a.i./ha fluazinam in broadcast application or in-furrow, and by 0.375 or 0.75 L a.i./ha flusulphamide applied in-furrow. In 2019, disease incidence and severity were significantly reduced by the broadcast application of fluazinam, and 75 kg/ha calcium cyanamide, but the latter had a negative impact on yield. Soil fumigation with metam sodium resulted in a 98% reduction in PS. Root galling was significantly reduced by calcium cyanamide, metam sodium, and fluazinam in the 2019 trial only. Foliar application of resistance-inducing phosphonates combined with fluazinam application had no additive effect on PS incidence and severity. Integrated approaches such as tolerant cultivars, soil testing, preplanting fungicide application, and sustainable means of control such as foliage cover for a short period may be implemented in order to control the disease and minimize damage.     

Association between elevated activity of aryl acylamidase and propanil resistance in Jungle-rice,Echinochloa colona

Aryl acylamidase (aryl-acylamine amidohydrolase, EC 3.5.1.13) activity has been measured in crude extracts from leaves of propanil-susceptible (S) and propanil-resistant (R) biotypes of the grass weed. Echinochloa colona (L.) Link from Columbia. Both specific and total amidase activity increased with plant age up to 15 days (four-leaf stage), then decreased beyond 20 days to about 50% of the maximum at 36 days in both R and S E. colona biotypes. Specific activity with propanil in the R biotype was about 80% of that obtained for rice (Oryza sativa L.), compared to 25% in the susceptible biotype. The specific activity of the propanil amidase was three-fold higher in the R biotype than in the S. Partially purified amidase extracts from rice and both S and R biotypes of E. colona were compared biochemically. Both rice and E. colona amidases had a pH optimum of 7.5 and native relative molecular masses, estimated by gel filtration, of 179 000 and 181 000, respectively. Out of six substrates tested, three produced appreciable activity (propanil, 4-chloroacetanilide and acetanilide) in both rice and E. colona. Michaelis constants showed that the rice amidase had a higher affinity for propanil (0.36 mM) than had the E. colona enzyme (1.1 mM). Carbamates and organo-phosphorus pesticides were shown to inhibit amidase activity in partially purified rice and E. colona extracts. Additional preliminary data have implicated peroxidase in the next step of propanil metabolism in vitro. These data demonstrate that increased aryl acylamidase activity contributes to resistance to the herbicide propanil in E. colona weeds. Also, a biochemical comparison of purified aryl acylamidases from S and R biotypes of E. colona is presented for the first time.     

Survey of Bacterial and Fungal Seedborne Diseases in Imported and Domestic Potato Seed Tubers

Potato seed tubers are imported to Israel from northern Europe and planted in spring; tubers harvested early from the spring crop are used as seed for the autumn crop. Although only seed lots registered as certified are imported, a previous survey (1984–1994) indicated that most imported lots were affected by latent or active infections caused byErwinia carotovora,Streptomyces scabies, Rhizoctonia solani, Fusarium spp. andSpongospora subterranae. The survey was extended until 1998, and included additional pathogens:Ralstonia solanacearum,Helminthosporium solani, Colletotrichum coccodes andVerticillium dahliae. Most of these pathogens were also monitored in domestic seed tubers, and are reported for the first time. Brown rot was not observed in any of the imported lots. Blackleg and soft rot caused byErwinia spp. were detected in most of the imported lots; however, less than 7% of the lots were contaminated at high levels, while approximately 65% were contaminated at moderate levels. Common scab was detected in most of the imported lots; 51% of the imported lots were contaminated at moderate or high levels, whereas only 6.5% of the domestic seed lots were contaminated at these levels. Black scurf was detected in most of the imported lots; on average, 47.3%, 44.2% and 1.4% of the lots were contaminated at low, moderate and high levels, respectively, and only 7.1% were disease-free. In contrast, most of the domestic lots were either disease-free (45.4%) or had a low disease incidence (37.3%). Only 16.7% of the lots were moderately infected and 0.2% were highly contaminated. Silver scurf was observed in most of the imported lots during all years of the survey, with no differences among the producing countries; on average, 22.7%, 66.1% and 7.5% of the lots were contaminated at low, moderate and high levels, respectively, and only 3.7% were disease-free. Most of the domestic lots (76%) were disease-free and only 6.6% were infected at moderate or high levels. Black dot was observed in a considerable portion of the shipments from Holland during all years of the survey, particularly in 1998, when 34% of the lots were infected. The shipments from France and Germany were infected at low levels, except in 1998, when 19% and 11% of the lots, respectively, arrived infected. In shipments from Scotland and Ireland low incidences of the disease were observed in 1994 and 1995. In the domestic lots, black dot incidence was low (<2.4%) except in 1996, when 11% of the lots were infected.V. dahliae was monitored only in domestic seed tubers. The incidence of disease-free lots was 56–64%, whereas in 20–30% of the lots the level of infection was <5%, and in 6–16% of the lots the level was >5%. The survey findings demonstrate transmission of seedborne pathogens; most of these pathogens can become established in the soil and eventually cause severe outbreaks of disease in potatoes grown in Israel. http://www.phytoparasitica.org posting May 16, 1999.     

Flow‐mediated movement of freshwater catfish,Tandanus bostocki,in a regulated semi‐urban river,to inform environmental water releases

Movement and migration of fish are critical for sustaining riverine fish populations. Water resource development alters natural flow regimes and can disconnect habitats and interfere with hydrological cues for fish movement. Environmental flow releases can counter these impacts, but to be effective they must be based on quantitative flow–biota relationships. We used radio‐telemetry to investigate the association between flow and movement of Tandanus bostocki, a plotosid fish endemic to south‐western Australia. Movement was assessed for 15 adult fish at three temporal scales: weekly, daily and bihourly to reveal seasonal patterns in movement, movement around individual flow pulses, and to describe changes in home range respectively. We used a predictive modelling approach to assess the importance of discharge and other covariates on the directional distance travelled or linear home range size. Our seasonal and flow pulse study revealed that T. bostocki undertook larger downstream movements during higher flows and smaller upstream movements during lower flows. Daily movements tended to be downstream on the ascending limb of flow pulses and upstream on the descending limb. Flow‐dependent movements at weekly or daily time scales were relatively modest (typically hundreds of metres) and were moderated by time of year and gender; however, fish underwent a synchronised 1‐km movement upstream during the known reproductive period in October. The home range study revealed that T. bostocki had larger home ranges (night‐time foraging) when baseflow was elevated. These results can assist the design of customised environmental flows in the study river and other flow‐regulated rivers.     

Age-related mechanisms of propanil tolerance in Jungle-rice,Echinochloa colona

Uptake and metabolism of propanil were measured in both susceptible (S) and resistant (R) biotypes of Jungle-rice, Echinochloa colona (L.) link at different growth stages. Results showed that there was no significant difference in uptake between S and R biotypes of E. colona at any given growth stage, but that uptake was significantly reduced at older plant growth stages in all biotypes studied. Metabolism of propanil was more rapid in R biotypes than in S biotypes at all growth stages studied. Specific and total aryl acylamidase activity, responsible for the first stage of propanil metabolism, was higher in R biotypes than in S at all growth stages, but declined to about 50% of the maximum at older growth stages, confirming the importance of this enzyme in conferring resistance to this herbicide. The area of necrosis that developed around a single drop of propanil deposited on the adaxial leaf surface was used to assess the degree of propanil resistance; it was found that resistance increased at older E. colona growth stages in contrast to the rate of propanil metabolism and amidase activity. Treatment of leaves with the amidase inhibitors, carbaryl or piperophos, simultaneously with propanil, caused a decrease in resistance at growth stages where amidase activity was greatest. This treatment was less effective at older growth stages. These results show that, in E. colona, propanil metabolism is important for conferring resistance in younger plants (four-six-leaf stage). It is suggested that restricted uptake confers resistance in older plants.