Phytotoxicity of Extracts of Argemone mexicana and Crotalaria longirostrata on Tomato Seedling Physiology.

Phytotoxicity caused by secondary metabolites of botanical extracts is a drawback in agriculture. The objective of this study was to evaluate the phytotoxic effects of methanolic extracts of Crotalaria longirostrata and Argemone mexicana on the germination and physiological variables of tomato seedlings. The results indicated that high doses of both extracts (Clong500 and Amex500) inhibited tomato seed germination, while their mixture (Cl50 + Am50) promoted germination by 100%. At 30 days after transplanting (dat), the plant height increased by 15.4% with a high dose of C. longirostrata (Clong500) compared to the control. At 30 dat, the vigor index displayed a notable increase with Cl50 + Am50, reaching 29.5%. The root length increased with the mean dose of A. mexicana (Amex95) at 10, 20, and 30 dat (59.7%, 15.1%, and 22.4%, respectively). The chlorophyll content increased with Amex95 by 66.1% in 10 dat, 22.6% at 20 dat, and 19.6% at 30 dat. On the other hand, Amex95 had a higher nitrogen content throughout the trial. Amex95 produced the greatest increase in root dry weight by 731.5% and 209.4% at 10 and 20 dat. The foliage dry weight increased by 85.7% at 10 dat with Amex95 and up to 209.7% with Amex50 at 30 dat. The present investigation reveals the ability of the extracts to stimulate tomato growth at low and medium doses, though at high doses they exhibit allelopathic effects.

First report of Fusarium equiseti causing root and crown rot in tomato in Mexico.

Tomato (Solanum lycopersicum L.) is one of the most important crops in Mexico due to its economic and nutritional value. Among the main diseases in tomato production is Fusarium wilt, which can cause 60% production losses (Ascencio et al, 2008). Mixed infections of Fusarium species or other fungi genera, would increase disease severity. During April to May of 2021, tomato plants with more than 60 days old, were collected from the main production areas of Aguascalientes (22°03'46.5"N 102°05'17.4"W and 22°04'53.64"N 101°58'55.81"W) and Zacatecas (23°05'59.2"N 102°41'07.3"W and 22°16'52.1"N 102°00'11.8"W) Mexico states. Plants showed main root rot, vascular bundles necrosis with corky appearance, stem crown rot, and ascending yellowing. The main root and stem crown were cut in 0.25 cm2 pieces and disinfested in 2% NaClO for one minute, rinsed with distilled water two times, placed on acidified potato dextrose agar (PDA) medium, and incubated at 25 ± 2°C for 7 days. Characteristic Fusarium growths were purified by hyphal tip on PDA, subsequently pure strains were obtained by single-spore isolation method. Several fungi colonies were obtained, but we focused on the colonies that showed abundant aerial mycelium of white color and irregular growth, which turned yellowish to golden and brown color as it ages. Carnation leaf agar (CLA) medium were used for conidia and sporodochium development. Chains of terminal, intercalary and agglomerated chlamydospores with thick, rough brown walls of 18.9 (7.46) µm in diameter (n=120) were observed in the mycelium. Macroconidia with 5 to 7 septa were 30 to 75 (28.32) µm in long and 1.2 to 4.8 (3.2) µm in wide (n=72). Basal cell developed in foot-shape, apical cell was elongated and slightly curved, and some macroconidia had swollen midd-cell. Sporodochium was orange to brown in color and microconidia were absent (Figure 1). Two representative strains from each state, LCA-3.1 and EMA-1 from Aguascalientes and ECZ-4 and LRZ-6 from Zacatecas, were selected for DNA amplification of ITS, TEF-1α and RPB2 regions, with universal primers ITS1/ITS4, EF1/EF2 and 2-5F2/7cR (White et al.1990; O'Donnell et al. 1998, 2013). PCR products were sequenced by Psomagen, Inc. (USA). The sequences obtained showed 100% of similarity among themselves and within species of the Fusarium incarnatum-equiseti species complex (FIESC) with nucleotide NCBI accessions NR_121457 (Type material) for ITS and MW362069 for TEF-1α; and 99.28% with MN170399 for RPB2 in FUSARIOID-ID database. According to morphological (Leslie and Summerell, 2006) and molecular characteristics, isolates were identified as Fusarium equiseti (FIESC 14). The LCA-3.1 sequences were selected to be deposited in GenBank with accession numbers OM812801 (ITS), OM937108 (TEF-1α) and ON653596 (RPB2). Pathogenicity tests were performed twice, under greenhouse conditions in tomato seedlings of cv. Rio Grande. Five tomato seedlings were inoculated by root immersion method (Lopez et al, 2018) in a 1x106 spores/mL solution for 8 min, and transplanted to 1L pots with sterile peat. Five controls plants were immersed in sterile water. At 14 days after inoculation, a general plant decline and slower growth compared to the control plants were observed. Subsequently, plants showed root rot, vascular necrosis, and a brown ring in stem crown. Controls were symptomless. The fungi were re-isolated from symptomatic plants and were morphologically similar to the inoculated strains. Patel et al. (2017) described the pathogenic and toxic effects of F. equiseti on tomato, causing low seed germination, and low root and shoot growth. This is the first report of F. equiseti causing root and stem rot in tomato plants in Mexico.

First report of Clonostachys rosea causing root rot on garlic in Mexico.

Garlic (Allium sativum) is an important crop worldwide and it is widely grown and used in different industries to manufacture food, pharmaceutical, and insecticidal products. (Shang et al., 2019, Velsankar et al., 2020). According to what was reported by SIAP in 2020, more than 87 ha of the crop were lost in Mexico due to various problems, including the diseases that attack this crop such as basal rot, white rot and root rot, among others. During the 2019 fall/winter season, garlic plants of Perla and Piedra Blanca cultivars were collected from Aguascalientes and Zacatecas states in San Antonio Tepezala, Rincon de Romos, and Calera municipalities. The commercial fields encompassed 10 ha with 20% disease incidence and 35% severity, approximately. The sampling focused on diseased plants with symptoms of root rot, foliar wilt, stunting, and small bulbs. The roots of 25 plants were cleaned, and portions of the diseased tissue were cut and disinfected in sodium hypochlorite at 1% for three minutes. They were rinsed twice with sterile water and dried with paper towels. The plant tissue was plated onto potato dextrose agar (PDA) and incubated at 25°C in the dark for 72 hours. Pure cultures were obtained after observing mycelial growth using monosporal culture. We obtained 16 isolates including three identified as Fusarium oxysporum, one as Fusarium solani and another 12 as Clonostachys rosea. The latter isolates were white at the beginning before turning yellow. The mycelia had a felt-like cotton texture. The conidia formed verticillate and penicillate conidiophores. The primary conidia were abundant, hyaline, smooth, and sub-globous. They were 5.1-7.7 X 8.3-8.9 µm (n=50) long and 2.0-2.9 X 3.2-3.5 µm wide (n=50). The conidiophore stipe length ranged from 70 to 180 µm, and the base width was 3.3-5.4 µm. Secondary conidiophores were penicillate and stiped with a length of 58 to 106 µm; the base measured 3.3-6.1µm. The secondary conidia measured 4.1-5 X 5.3-5.6 µm long and 2-2.3 X 2.6-2.9 µm wide (n=50) (Sun et al., 2020). The identity of six isolates was molecularly confirmed by DNA extraction and PCR reactions using ITS1/ITS4 primers and gene TEF 1α EF1-728F/TEF 1α EF1-986R. The resulting products were sequenced and compared with the National Center for Biotechnology Information (NCBI) database using BLAST. The results showed Clonostachys rosea at 99.56 and 100% with access numbers MN548399 and KX185000. The sequences were deposited at Genbank database under access number OK263088 and OL700031. Pathogenicity tests were carried out with the following procedure. A conidial suspension of five isolates (5×105 conidia/ml) in sterilized water was prepared from 1-week-old colonies. The garlic cloves were planted after being disinfected with sodium hypochlorite at 1% in sterilized soil. When the healthy garlic plants were 30 days old, we inoculated a spore suspension in soil through irrigation, to 10 plants. Likewise,10 control plants were inoculated with sterile distilled water. After 25 days, the plants were wilted and had dry leaves; their root system showed light-brown lesions and rot. These plants were stunted versus the control healthy plants. The inoculated strain was recovered and was morphologically and molecularly identified as C. rosea, thus confirming its pathogenicity towards garlic. There are reports of C. rosea causing root rot to Fabaceae crops such as Glycine max L. and Vicia faba L., (Bienapfl et al., 2012; Afshari and Hemmati, 2017) in addition to affecting orchid crops (Gastrodia elata) in Korea (Lee et al., 2020). This is the first report of C. rosea causing root rot on garlic (Allium Sativum) in Mexico, thus presenting a potential risk to this crop.