Aphelenchoides besseyi parasitizing tobacco cultivars in Brazil

Foliar nematodes, Aphelenchoides spp., are known to be parasites of tobacco in restricted areas, but symptoms caused by A. besseyi in tobacco are not well characterized, depite the great importance of this nematode worldwide. This study aimed to evaluate the host reaction of four Nicotiana tabacum cultivars (Comum, Xanthi, Samsun, and TNN) and N. benthamiana cv. Comum to A. besseyi and to characterize the symptoms and the parasitism of this nematode. Two experiments were conducted under greenhouse conditions with controlled humidity and temperature, in which the plants were inoculated with 600 A. besseyi. At 30 days after inoculation (DAI), nematodes present in the soil, roots and shoot parts were extracted and roots and shoot tissues were stained with acid fuchsin. High number of A. besseyi was obtained per gram of shoot tissues (125 - 2,169 nematodes) and severe symptoms were observed in leaves and inflorescences of all cultivars. Symptoms included foliar distortion and deformation, necrotic spots delimited by the veins, flower abortion and poor development of plants. In addition, A. besseyi was observed to penetrate tobacco roots at 30 DAI, and nematodes were also observed in the foliar mesophyll, inflorescences, and stems, a parasitism that has not been previously reported in tobacco plants. The disease caused by A. besseyi in tobacco could be a concern for growers in Southern and Northeastern Brazil because this nematode can cause severe damage to the marketable leaves of tobacco, reducing its commercial value.

Feeding Selectivity of Aphelenchoides besseyi and A. pseudogoodeyi on Fungi Associated with Florida Strawberry

Aphelenchoides besseyi and A. pseudogoodeyi are foliar nematodes associated with commercial strawberry production in Florida, United States. The reproductive and feeding habits of these two nematode species were assessed on Florida isolates of the fungi Botrytis cinerea, Colletotrichum gloeosporioides, Macrophomina phaseolina, and Neopestalotiopsis rosae, which are pathogenic to strawberry, and nonpathogenic isolates of Fusarium oxysporum and Monilinia fructicola grown on potato dextrose agar in Petri dishes. Each culture was inoculated with six specimens of mixed life stages of A. besseyi or A. pseudogoodeyi and incubated at 24°C under axenic and nonaxenic conditions 23 and 31 days after inoculation, respectively. A. besseyi reproduction rates were greater on strawberry-pathogenic isolates of B. cinerea, C. gloeosporioides, and N. rosae than on the nonpathogenic isolates of F. oxysporum and M. fructicola. In contrast, reproductive rates of A. pseudogoodeyi did not vary among fungi cultures. For both nematode species, M. phaseolina was a poor host because it did not produce mycelium on the media used. Our findings indicate that A. besseyi is more selective in its fungal-feeding preference than A. pseudogoodeyi. Additionally, A. pseudogoodeyi eggs and juveniles were significantly more numerous than adults. Yet, for A. besseyi, adult stages were more abundant. Fungi aid in the maintenance of soil-dwelling populations of these two nematode species. Removing fungus-infected strawberry plant residues is both a desirable and effective management practice to limit A. besseyi in central Florida commercial strawberry fields.

Aphelenchoides besseyi Parasitizing Cowpea (Vigna unguiculata) in Brazil

Several species of nematodes are known to cause losses to cowpea (Vigna unguiculata) throughout the world. In Brazil, Aphelenchoides besseyi was described as causing damage on soybean, cotton, and common bean, but no report was found about the parasitism of this nematode in cowpea. This study aimed to verify the host reaction of cowpea cultivars to A. besseyi. The experiment was conducted under greenhouse conditions, using two A. besseyi populations as inocula, obtained from symptomatic soybean and cotton plants collected in naturally infested fields. Cultivars Imponente, Aracê, Guariba, Tumucumaque, Nova Era, and Tracuateua were inoculated with 500 A. besseyi of each population, separately, into soil, and after 30 days from the inoculation nematodes were extracted from shoot systems. Both populations were able to parasitize all the cowpea cultivars. Independently of the cultivar, cowpea plants exhibited symptoms of leaf deformation similar to those described for soybean, cotton, and common bean and, in addition, severe brooming was observed, with the interior of the stems being porous and necrotic. To our knowledge, this is the first report of parasitism by A. besseyi of cowpea in Brazil, under greenhouse conditions, increasing the list of hosts of this nematode.

Aphelenchoides besseyi Parasitizing Common Bean in Brazil

Aphelenchoides besseyi is the causal agent of soybean green stem and foliar retention syndrome known as "Soja Louca II." This nematode has recently been reported parasitizing cotton in Brazil. In Costa Rica, it causes the symptoms known as "amachamiento" and false angular spots in common bean (Phaseolus vulgaris). Due to the great importance of beans to Brazilian agriculture, the objective of this research was to study the pathogenicity of A. besseyi in common bean under greenhouse conditions, including its endoparasitic relationships by staining root and shoot system tissues with fuchsin acid. In addition, A. besseyi was collected and quantified from shoot systems 30 days after inoculation by washing the tissue in water and blender centrifugal flotation. We observed the symptoms of amachamiento, leaf and vein deformation in the expanded trifoliate leaves, and also leaves with necrotic, brown to reddish and angular lesions, characteristics from false angular spot, and deformed stems characterized by enlargement of nodes, retortions, and necrotic lesions. High numbers of nematodes were found inside common bean plants. This is the first report of the pathogenicity and symptoms caused by A. besseyi in common bean in Brazil. These findings are important for development of management strategies to avoid losses on bean cropped in infested areas.

Population Dynamics and Dispersal of Aphelenchoides fragariae in Nursery-grown Lantana

Population dynamics of Aphelenchoides fragariae were assessed over three growing seasons and during overwintering for naturally-infected, container-grown lantana (Latana camara) plants in a North Carolina nursery. During the growing season, the foliar nematode population in symptomatic leaves peaked in July each year then remained above 100 nematodes/g fresh weight into late summer. Foliar nematodes were also detected in asymptomatic and abscised leaves. Results suggest that leaves infected with foliar nematodes first develop symptoms at populations of about 10 nematodes/g. Foliar nematodes were detected in symptomatic and asymptomatic plant leaves and in abscised leaves during overwintering in a polyhouse, but the number of infected plants was low. A steep disease gradient was found for infection of lantana plants by A. fragariae on a nursery pad with sprinkler irrigation. When the canopies of initially healthy plants were touching the canopies of an infected plants, 100% of the plants became infected within 11 wk, but only 5 to 10% became infected at a canopy distance of 30 cm. Overwintering of A. fragariae in infected plants and a steep disease gradient during the growing season suggests strict sanitation and an increase in plant spacing are needed to mitigate losses from this nematode pest.

Conventional and PCR Detection of Aphelenchoides fragariae in Diverse Ornamental Host Plant Species

A PCR-based diagnostic assay was developed for early detection and identification of Aphelenchoides fragariae directly in host plant tissues using the species-specific primers AFragFl and AFragRl that amplify a 169-bp fragment in the internal transcribed spacer (ITS1) region of ribosomal DNA. These species-specific primers did not amplify DNA from Aphelenchoides besseyi or Aphelenchoides ritzemabosi. The PCR assay was sensitive, detecting a single nematode in a background of plant tissue extract. The assay accurately detected A. fragariae in more than 100 naturally infected, ornamental plant samples collected in North Carolina nurseries, garden centers and landscapes, including 50 plant species not previously reported as hosts of Aphelenchoides spp. The detection sensitivity of the PCR-based assay was higher for infected yet asymptomatic plants when compared to the traditional, water extraction method for Aphelenchoides spp. detection. The utility of using NaOH extraction for rapid preparation of total DNA from plant samples infected with A. fragariae was demonstrated.

Infection Behavior and Overwintering Survival of Foliar Nematodes, Aphelenchoides fragariae, on Hosta

We studied the pathogenicity and overwintering survival of the foliar nematode, Aphelenchoides fragariae, infecting Hosta spp. Nematodes applied to either lower or upper sides of noninjured and injured hosta leaves were able to infect and produce typical symptoms on nine cultivars. Leaves of only four cultivars (Borschi, Fragrant Blue, Patomic Pride, and Olive Bailey Langdon) showed no symptoms of nematode infection. The nematodes overwintered as juveniles and adults in soil, dry leaves, and dormant buds, but not in roots. Nematode winter survival was higher in dormant buds and soil from the polyhouse than in an open home garden. Of the nematodes found in the dormant buds, 35% to 79% were located between the first two outside layers of the buds. The nematodes tolerated 8 hr exposure to 40 degrees C and -80 degrees C in leaf tissues. Relative humidity influenced nematode migration from soil to leaves. The presence of nematodes only on the outer surface of foliage (leaves and petioles) confirmed the migration of A. fragariae on the surface of the plants. Of the total number of nematodes found on the foliage, 25% to 46% and 66% to 77% were alive at 90% and 100% relative humidity, respectively, suggesting that high moisture is required for the survival and upward movement of nematodes. We conclude that A. fragariae can overwinter in soil, infected dry leaves, and dormant buds and migrate in films of water on the outer surface of the plant during spring to leaves to initiate infection.

Effectiveness of a Hot Water Drench for the Control of Foliar Nematodes Aphelenchoides fragariae in Floriculture

Effectiveness of a hot water drench for the control of Aphelenchoides fragariae infesting hosta (Hosta sp.) and ferns (Matteuccia pensylvanica) was studied. Drenching with hot water at 70 degrees C and 90 degrees C in October reduced (P < 0.05) A. fragariae in the soil but not in the leaves relative to the control (25 degrees C) 300 days after treatment (DAT). Plants drenched with 90 degrees C water had lower numbers of nematode-infected leaves per plant than those treated with 25 degrees C and 70 degrees C water (P < 0.05). Hot water treatments had no adverse effect on the growth parameters of hosta. Boiling water (100 degrees C) applied once a month for 3 consecutive months (April, May, June) consistently reduced the number of infected leaves and the severity of infection relative to the control 150 DAT in hosta but not in ferns (P < 0.05). Boiling water (100 degrees C) caused a 67% reduction in A. fragariae population in hosta leaves, 50% in fern fronds, and 61% to 98% in the soil over the control 150 DAT. A boiling water drench had no effect on the fern growth but caused 49% and 22% reduction in the number and size of hosta leaves, respectively, over the control in 2002. We conclude that 90 degrees C water soil drench in the autumn or early spring could prove effective in managing foliar nematodes on hosta in nurseries and landscapes.

Refinement of Hot Water Treatment for Management of Aphelenchoides fragariae in Strawberry

The effects of hot water treatments on a California population of the foliar nematode, Aphelenchoides fragariae, and on five strawberry cuttivars ('Chandler', 'Douglas', 'Fern', 'Pajaro', and 'Selva') were assessed in laboratory and greenhouse tests. Nematodes extracted from fern leaves were placed in water maintained at 44.4, 46.1,47.7, or 49.4 C for different time periods. Exposure periods of 15, 5, 4, and 2 minutes were required to produce 100% mortality at 44.4, 46.1, 47.7, and 49.4 C, respectively. In a water bath, 4 minutes were required for strawberry crowns initially at 25 C to equilibrate with temperatures ranging from 44.4-54.4 C. The maximum exposure periods that did not significantly reduce subsequent plant growth and flowering were 30, 15, and 10 minutes, at 44.4, 46.1, and 47.7 C, respectively. Survival of Selva was lower (P = 0.05) than for the other cultivars. Treatment at 49.4 C for 5 minutes significantly reduced plant growth and flowering of all cultivars. The minimum-maximum exposure periods that killed A. fragariae without damaging the cultivars tested were 20-30 minutes at 44.4 C, 10-15 at 46.1 C, or 8-10 at 47.7 C.