Cercospora Leaf Spots of Wheat in the Lowland Tropics of Santa Cruz, Bolivia
Mario Coca Morante*
Plant pathology laboratory, Phytotechnician department. Faculty of Agricultural, Livestock and Forestry Sciences. Universidad Mayor de San Simón. Cochabamba, Bolivia
Submission: February 01, 2024; Published: February 23, 2024
*Corresponding author:Mario Coca Morante, Plant pathology laboratory, Phytotechnician department. Faculty of Agricultural, Livestock and Forestry Sciences. Universidad Mayor de San Simón. Cochabamba, Bolivia
How to cite this article: Mario Coca Morante. Cercospora Leaf Spots of Wheat in the Lowland Tropics of Santa Cruz, Bolivia. Agri Res& Tech: Open Access J. 2024; 28(2): 556403 DOI: 10.19080/ARTOAJ.2024.28.556403
Abstract
The cultivation of wheat (Triticum aestivum L.) in the lowland tropics of Santa Cruz department in Bolivia is recent. Leaf spots diseases are an important yield-reducing factor. Since 1996, Pyricularia blast wheat is the most destructive disease in tropical regions producing wheat. In 2023, sampling was carried out in different locations in the East (Cuatro cañadas) and North (Okinawa1, Okinawa2) production wheat of Santa Cruz. Leaf, sheath and glumes simples were analyzed under microscopy and were estimated incidence. Two Cercospora species, C. oryzae and C. sorghi, were recorded associated with the leaf spots of 'Motacu' variety and these leaf spots seem to be prevalent and widely distributed in the production wheat áreas in the lowland tropics of Santa Cruz, Bolivia.
Keywords: wheat leaf spots, C. oryzae and C. sorghi, new disease.
Introduction
In the lowlands tropics of the Santa Cruz department, the cultivation wheat (Triticum aestivum L.) began to expand between 1985-1990.In 2022, one 120,000 to 140,000 has were cultivated (INE 2023). Main leaf spot diseases causing losses in wheat production in the north and eastern Santa Cruz región are Septoria leaf and glume spots (Septoria tritici and Septoria nodorum) and spot blotch (Cochliobolus sp). Barea and Toledo (1996) reported Pyricularia wheat blast in Santa Cruz Department of Bolivia [1]. Currently, Pyricularia blast wheat is the most destructive leaf spot for wheat production in the Santa Cruz lowland tropics. According to Xinyao et al. [2], some major non-rust diseases of wheat with global and/or regional economic importance are addressed, including three spike diseases (Fusarium head blight, wheat blast, and Karnal bunt), four leaf spotting diseases (tan spot, Septoria nodorum blotch, spot blotch, and Septoria tritici blotch). Other foliar diseases that affect the wheat, were not reported. During the agricultural year wheat (2023), other leaf spots were observed that were affecting commercial wheat production. The objetives of this research were: i. To identify the casual agent of the leaf spot of wheat; and, ii. To estimate the “unknown” leaf spot incidence.
In August 2023, sampling was carried out in commercial production winter wheat (ˈMotacuˈ variety) production areas at the harvest stage in two winter wheat-producing municipalities (April-August) in the lowlands of the Santa Cruz department: Okinawa in the Warnes Province and Cuatro cañadas in the Ñuflo de Chavez Province. In Olkinawa two localities were sampled: Okinawa 1 (262 meters above sea level, 20K 510442 and UTM 8091262) and Okinawa 2 (271 masl, 20K 517888 and UTM 8085843), in the Okinawa municipality, Warnes Province. In Cuatro Cañadas one sample were collected in this municipality (267 masl, 20k 531485 and UTM 8098189). Samples were taken from a 1 m2 area. Three 1m2 replicates were randomly set in each sampled field. Each sample was cut manually with a sickle at the height of the stem base, was identified and transferred to the laboratory. Each sample was evaluated independently for symptoms and signs. The identification of the causal agent was carried out by mounting microscopics slides using lactophenol solution based on morphological characters in vivo and analyzing conidiophores and conidia according to Chupp [3], Ellis [4] and Braun et al. [5]. The incidence of disease was assessed according to Campbell and Madden [6] [% Incidence (Total diseased plants/total number plants*100)] and was carried out on each plant under a stereomicroscope, checking leaf, stem, glume, and spike.
Two types of symptoms were found: linear spots (Figure 1A, B,C,D) and elliptical leaf spots (Figure 1G,H). The linear spots are dark brown, with variable length, average 2-10 x 1-2 mm, parallel to the midrib or the leaf veins of leaves (Figure 1A), sheaths (Figure 1B-C), and glumes base (Figure 1D). Conidiophores emerge through the stomata in linear form over the symptoms and amphigenous locating fruiting bodies were present (Figure 1C), being sometimes dense in fascicles, brown or dark brown, 1-2-septate, slightly attenuated at the tip (Figure 1E-F), with 1-2 mild geniculations and, 1-3 thickened scars (Figure 1F), 30-70 x 3.5-4 µm. Conidia are hyaline, cylindrical to obclavate, straight or slightly curved, 3-4 septate, obconic at base having thick dark scar, obtuse at apex, 12-60 x 2.5-3µm. Conidiophore and conidia associated registered for these leaf spot are coincident to Cercospora oryzae Myake, described by Chupp [4], Sphaerulina oryzina Hara (Syn. C. oryzae) by Ellis [5] and Syn. Cercospora janseana according Braun et al. [5], causing narrow Brown spot.
The elliptical leaf spots had sharp or rounded edges (Figure 1G), with center pale and margin brown (Figure 1H), amphigenous fruiting bodies, fascicle dense at the center (Figure 1I-J), stromata dark Brown; conidiophores brown in color, slighthy paler and narrow toward the tip, 1-3 septate, attenuated at the tip, slightly undulated, scare rounded tip (Figure 1I-J); conidia hyaline 35-120 x 3-3.5µ, acicular to obclavate, straight to mildly curved, mostly 1-4 septate (longest ones may have 8 septa) not catenulate, ápex subacute, base truncated or usually long obconic, tip subacute to acute 3-3.5 x 15-60µ (Figure 1K). Conidiophore and conidia associated with the Cercospora leaf spot are coincident to Cercospora sorghi Ellis & Everhart described by Chupp [4], Ellis [5] and Braun et al. [3]. According to these authors C. sorghi is widely distribuited in tropical and subtropical countries affecting leaves of grasses. On the other hand, Metha [7] and Xinyao et al. [2] are not report Cercospora leaf spot affecting wheat. The incidence of Cercospora leaf spots in wheat was recorded in the three sampled locations (Cuatro cañadas-3.96%, Okinawa2-9.7%, and Okinawa1-16.45%), being higher in Okinawa1, probably due to the higher environmental humidity prevalent during the study.
Conclusion
In conclusion, two Cercospora species were recorded for the first time affecting the leaf, sheath, and glume wheat in different degrees of incidence in the production wheat area in the lowland tropics of Santa Cruz, Bolivia.
Acknowledgment
The author thanks the cooperation to the Engineer Agronomist Lucas Vittorio Aguilar, technical Crop Protection Development. Syngenta Crop Protection S.A. Santa Cruz, Bolivia, for his cooperation in collecting samples of wheat from the north and east locations of the department of Santa Cruz. To the Agronomist Jr. Juan Daniel Vargas, temporary intern, fot his help in several field activities, and also to the producers of the sampled locations. To Eduardo SG Mizubuti Dr., Departamento de Fitopatología, Universidad Federal de Viçosa 36570-900 Viçosa, MG Brasil, for your revisión and sugestions to the manuscript.
References
- Kohli MM, Mehta YR, Guzman L, Viedma LD, Cubilla LE (2011) Pyricularia blast-a threat to wheat cultivation. Czech J Genet Plant Breed 47(10): S130-S134.
- Xinyao H, Navin CG, Chandan R, Abdelfattah AD, Gurcharn Singh B, et al. (2022) Chapter 9, Globally Important Non-rust Diseases of Wheat. Pp:143-158. In: Reynolds MP, Braun HJ (Eds.), Wheat Improvement. Food Security in a Changing Climate. pp. 658.
- Braun U, Crouss PW, Chiharu N (2015) Cercosporoid fungi (Mycosphaerellaceae) 3. Species on monocots (Poaceae, true grasses). IMA FUNGUS 6(1): 25-97.
- Chupp Ch (1953) A monograph of the Fungus Genus Cercospora. Ithaca, New York.
- Ellis MB (1976) More Dematiaceous Hyphomycetes. Commonwealth Mycological Institute. Kew, Surrey, England.
- Campbell CL, Madden LV (1990) Introduction to Plant Disease Epidemiology. John Wiley & Sons, New York.
- Mehta YR (2014) Chapter 3 Spike Diseases Caused by Fungi. pp:65-97. In: Wheat Diseases and Their Management. Springer International Publishing Switzerland. pp. 253.