RESUMO
Oat (Avena sativa L.) is a vital cereal crop and serves as food, feed, and industrial material for many commercial growers. The presence of root-lesion nematodes (RLN; Pratylenchus spp.) in oat-cultivated areas of China is alarming because RLNs display an endo-migratory life cycle and rank third among the most damaging nematode pests (Jones et al. 2013). Their penetration and feeding cause necrotic lesions on the roots, which further dispose plants to other soilborne pathogens resulting in extensive root rots (LaMondia, 2003). In China, it has been reported that P. thornei harmed sugarcane and wheat. (Fang et al 1994; Fan et al. 2020), However, there are no reports on the damage of P. thornei to oat. In June 2021, a survey of one oat field, exhibiting poorly developed plants reduced till number and distinct lesions on roots was conducted in Dingxi city, Gansu province, China (N 35°56', E 104°60'). Thirteen soil and root samples were collected from symptomatic plants (cultivar: Jizhangyan No.5). Nematodes were extracted from root and soil samples using the modified Baermann funnel method (Hooper, 1986). Twelve samples tested positive for the presence of RLN with population densities ranging from 3 to 25 juveniles and females/100 g of soil and 2 to 32/g of root. No males were detected. Twenty females from the twelve positive samples were selected at random and examined morphologically for species-level identification (Figure 1A-J). The female bodies were slender, almost straight or ventrally curved after heat relaxation (Figure 1A), labial region continuous with the rest of the body and bears three faint lip annuli. The stylets were short and stout with well-developed basal knobs (Figure 1C, G). The pharyngeal and reproductive components were typical of pratylenchid nematodes (Figure 1B). Tail region cylindrical, straight or curved ventrally, having variable terminus viz., broad, bluntly rounded or truncate, with no striations around terminus (Figure 1H-J). The diagnostic morphometrics of adult females were as follows: body length 591.4 ± 20.1 µm (466.6 to 742.7 µm), body width 22.5 ± 0.5 µm (20.1 to 26.2 µm), distance from anterior end to excretory pore 88.4 ± 3.5 µm (75.7 to 99.7 µm), stylet length 16.8 ± 0.2 µm (15.2 to 18.7 µm), and tail length 33.7 ± 1.3 µm (25.5 to 43.2 µm). De man's morphometric parameters were a: 26.3 ± 0.8 (19.8 to 31.1), b: 5.7 ± 0.2 (4.7 to 7.0), c: 17.9 ± 0.8 (12.9 to 23.7), c': 2.3 ± 0.1 (1.7 to 2.8) and V value was 77.8 % ± 1.2 (67.3 to 86.6 %). The morphological and morphometric characteristics of our detected population is consistent with Loof's 1960 description of P. thornei Sher and Allen, 1953 (Table 1). For molecular analysis, five females from the twelve positive samples were selected at random for molecular analysis. DNA was extracted from single females according to the method of Wang et al. (2011). The ITS region was amplified by primer pair 18S/26S (Vrain et al., 1992) and the D2/D3 expansion region of the 28S rDNA was amplified by primer pair D2A/D3B (Castillo et al., 2003). High quality PCR products of accurate fragment length were sent to the Tsingke Biological Technology (Xian, China) for sequencing. The ITS sequences (813 bp-817 bp, GenBank OP902282, OP902284, OP902287, OP902288 and OP902289) of Gansu population showed 99.26%-100% sequence identity with P. thornei reported from Italy (FR692299, FR692303 and FR692304) (Figure 2). The 28S sequences (738 bp-764 bp, GenBank OM278343, OP217988, OP218403, OP218404 and OP218567) showed 100% identity with P. thornei populations reported from Belgium (KY828302), the USA (OK490327) and Iran (JX261960) (Figure 3). Morphological and molecular data of the Gansu population obtained in this study supported its identification as P. thornei. The endo-migratory association of the host-nematode relationship was confirmed by observing nematodes inside the roots using acid fuchsin root staining (Wu et al. 2014) (Figure 4). Oat (cultivar: Jizhangyan No.5) seeds were sown in pots containing 500 g of naturally infested soil (an average of 12 P. thornei /100g of soil); autoclaved soil was used as a control. Fifty seeds were directly sown in pots (20 × 16 cm), with three replicates. Plants were maintained in an incubator at 28 ± 1°C (12 h/12 h light/dark). Results indicated that plants inoculated obviously grew poorly with some lesions on roots and P. thornei numbers in them increased 16 times both in soil (50.7 ± 9.6 nematodes/100g) and roots (708.0 ± 8.7 nematodes in the entire root system). No P. thornei was found in the control soil and roots (Figure 5). Morphological and molecular characteristics of specimens isolated from oat symptomatic roots (n = 10) were identical to P. thornei. The losses caused by P. thornei are still unknown, and considering Pratylenchus spp. are commercially important nematode, the more investigations on oats should be made in the future. As of yet, RLNs were not reported from any oat-cultivated areas of China. To our knowledge, this is the first report of P. thornei parasitizing oats in the Gansu province of China.
RESUMO
Snow pea root rot in China is caused by Fusarium solani (FSH) and Fusarium avenaceum (FAH), which affect snow pea production. The chemical control methods used against FSH and FAH are toxic to the environment and resistance may be developed in persistence applications. Therefore, an alternative approach is needed to control these pathogens. This study focuses on Trichoderma longibrachiatum strains (TL6 and TL13), mycoparasitic mechanisms of FSH and FAH, as well as growth-promoting potentials on snow pea seedlings under FSH and FAH stress at the physiological, biochemical, and molecular levels. The average inhibitory rates of TL6 against FSH and FAH were 54.58% and 69.16%, respectively, on day 7. Similarly, TL13 average inhibitory rates against FSH and FAH were 59.06% and 71.27%, respectively, on day 7. The combined TL13 and TL6 with FSH and FAH reduced disease severity by 86.6, 81.6, 57.60, and 60.90%, respectively, in comparison to the controls. The snow pea plants inoculated with FSH and FAH without TL6 and TL13 increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents in the leaves by 64.8, 66.0, 64.4 and 65.9%, respectively, compared to the control. However, the combined FSH and FAH with TL6 and TL13 decreased the MDA and H2O2 content by 75.6, 76.8, 70.0, and 76.4%, respectively, in comparison to the controls. In addition, the combined TL6 + FSH and TL6 + FAH increased the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) by 60.5, 64.7, and 60.3%, respectively, and 60.0, 64.9, and 56.6%, respectively, compared to the controls. Again, compared to the controls, the combined TL13 + FSH and TL13 + FAH increased the activity of SOD, POD, and CAT by 69.7, 68.6, and 65.6%, respectively, and 70.10, 69.5, and 65.8%, respectively. Our results suggest that the pretreatment of snow pea seeds with TL6 and TL13 increases snow pea seedling growth, controls FSH and FAH root rot, increases antioxidant enzyme activity, and activates plant defense mechanisms. The TL13 strain had the greatest performance in terms of pathogen inhibition and snow pea growth promotion compared to the TL6 strain.