Survey, Identification and Growth Behaviour of Fusarium oxysporum f. sp. psidii in Guava

1. Introduction cultivated widely in India due to its high nutritional value, adaptability and economic returns. It is a rich source of vitamin C, pectin and minerals, making it an essential component of human diet as well as the fruit processing industry. Despite its wide adaptability, guava production is significantly constrained by several biotic stresses, among which wilt disease is considered one of the most destructive and economically important (Gupta et. al., 2010) [6] . Guava wilt, primarily caused by Fusarium oxysporum f. sp. psidii, is a serious soil-borne disease affecting guava orchards in major growing regions. The disease is characterized by yellowing, drooping and eventual wilting of leaves, followed by complete plant death. Internally, the pathogen colonizes the vascular tissues, particularly xylem vessels, leading to blockage of water transport and subsequent plant mortality. The severity of the disease has been reported to cause substantial yield losses and, in severe cases, complete orchard decline, posing a major threat to sustainable guava cultivation. Understanding the distribution and incidence of the disease is essential for developing effective management strategies. Surveys conducted in different guava-growing regions have indicated that wilt disease is widely prevalent with varying intensity depending on agroclimatic conditions and orchard management practices. In Maharashtra, particularly in Ahilyanagar district, the disease has emerged as a significant constraint, necessitating systematic investigation into its occurrence and spread. Accurate identification of the causal pathogen is a prerequisite for devising appropriate control measures. Isolation of the pathogen from infected plant tissues using standard microbiological techniques, followed by its identification based on cultural, morphological and microscopic characteristics, remains a reliable approach. Fusarium oxysporum f. sp. psidii typically produces septate, hyaline mycelium along with two types of spores, viz., microconidia and macroconidia, which serve as key diagnostic features. Further, studies on morphological, cultural and physiological characteristics of the pathogen provide valuable insights into its growth behavior, survival and pathogenic potential. Evaluation of growth on different culture media and under varying environmental conditions helps in understanding the biology of the pathogen, which is crucial for developing effective disease management strategies.

Survey for wilt of guava disease.

A roving survey was conducted during 2025 in Ahilyanagar district, Maharashtra, to assess the incidence of Fusarium wilt of guava. Diseased root samples showing typical symptoms such as vascular browning, root decay and plant wilting were collected from different locations. Disease incidence was calculated based on the number of infected plants over the total plants observed. The results indicated that wilt disease was prevalent across all surveyed talukas, with incidence ranging from 2.27 to 7.14 per cent. The lowest incidence was recorded in Rahuri taluka (2.27-2.97%), whereas the highest was observed in Rahata taluka (3.80-7.14%). In Newasa and Shrirampur talukas, disease incidence ranged from 2.85 to 4.37 per cent and 3.18 to 4.46 per cent, respectively. Overall, the survey revealed that guava wilt is a widespread and significant disease in the region. These findings are in agreement with earlier reports identifying wilt as a major constraint in guava cultivation. [Gupta and Misra (2012) [5,7,9]

Isolation of pathogen causing wilt of Guava.

Samples of diseased guava plants according to their symptoms were collected during survey form different tahsil of Ahilyanagar district. Isolation was carried out by tissue segment method on potato dextrose medium. By using culture plates, the pathogen was cultured, purified and maintained on PDA petri plates for subsequent experiment. Identification of the pathogen was carried out based on symptomatology, cultural and morphological characteristics, microscopic observations and pathogenicity tests. The fungus exhibited white mycelial growth initially, which later turned pink on PDA. Microscopic examination revealed aseptate, elliptical microconidia and 3-4 septate, sickleshaped macroconidia, confirming the pathogen as Fusarium oxysporum f. sp. Psidii. These findings align with those reported by Pandey and Dwivedi (1985) [12] isolated and identified Fusarium oxysporum f. sp. psidii from roots of guava plants.

Morphology of isolated pathogen

The pathogen Fusarium oxysporum f. sp. psidii produced septate, hyaline mycelium, initially white which later turned pink (Plate 1). Microscopic examination revealed abundant microconidia and macroconidia. Microconidia were mostly aseptate, oval to elliptical, measuring 4-9 × 1-3 µm (Plate 2), while macroconidia were 3-4 septate, sickle-shaped, thin-walled and measured 15-24 × 2-5 µm (Plate 3). Variations in conidial size were observed among different isolates (Table 2). The present findings on morphological characteristics of Fusarium oxysporum f. sp. psidii are in agreement with earlier reports by Dubey et al. (2010) [2] , Nikam et al. (2011) [11] and Mamta et al. (2013) [10] . The growth of Fusarium oxysporum f. sp. psidii was evaluated at different temperatures. Maximum growth was observed at 25°C (79.99 mm), followed by 30°C (76.53 mm), while minimum growth was recorded at 5°C (9.39 mm). Reduced growth was also observed at lower temperatures (10-15°C) (Table 3, Plate 4). These results indicate that 25-30°C is the optimum temperature range for pathogen growth and are in agreement with earlier findings.

[ Gaurav (2013) and Chavan ( 2007)] [4,11] .

Effect of pH on growth of Fusarium oxysporum f. sp. Psidii

The growth of Fusarium oxysporum f. sp. psidii was studied under different pH levels. Maximum growth was observed at pH 6.5 (85.69 mm), followed by pH 6.0 and 7.0, while minimum growth was recorded at pH 8.5 (75.35 mm). Growth decreased under alkaline conditions, indicating that slightly acidic to neutral pH (6.0-7.0) is optimum for pathogen growth. Among isolates, higher growth was recorded in Fs-1, Fs-2 and Fs-3, whereas Fs-4 showed the least growth at higher pH (Table 4, Plate 5). These results are in agreement with earlier findings. [Farooq et al. (2005), Chavan (2007)] [1] .

Conclusion

The present investigation revealed that guava wilt is a widespread and significant disease in Ahilyanagar district, with variable incidence across different locations. The pathogen associated with the disease was successfully isolated and identified as Fusarium oxysporum f. sp. psidii based on cultural, morphological and microscopic characteristics. Symptomatological studies confirmed typical vascular wilt symptoms leading to plant decline and death. Physiological studies indicated that the pathogen exhibited maximum growth at 25-30°C and at slightly acidic pH (around 6.5), while Richard's agar was found to be the most suitable medium for its growth and sporulation. These findings provide important insights into the biology and ecology of the pathogen, which can be useful for developing effective management strategies for guava wilt.

References

1. Chavan SS. Studies on fungal diseases of Patchouli with special reference to wilt caused by Fusarium solani (Mart.) Sacc. M.Sc. (Agri.) thesis submitted to College of Agriculture, Dharwad University of Agricultural Sciences, Dharwad; 2007.
2. Dubey SC, Singh SR, Singh B. Morphological and pathogenic variability of Indian isolates of Fusarium oxysporum f. sp. ciceri, causing chickpea wilt. Arch Phytopathol Plant Protect. 2010;43(2):174-190.
3. Farooq S, Iqbal M, Rauf A. Physiological studies of Fusarium oxysporum f. sp. ciceri. Int J Agric Biol. 2005;7(2):275-277.
4. Gaurav V. Studies on Fusarium moniliforme a causal organism of bakanae disease of rice. M.Sc. thesis, Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (U.P.); 2013.
5. Gupta VK, Misra AK. Fusarium chlamydosporum, causing wilt disease of guava (Psidium guajava L.) in India. Arch Phytopathol. 2012;45:2425-2428.
6. Gupta VK, Misra AK, Gaur RK, Jain PK, Gaur D, Sharma S. Current status of Fusarium wilt disease of guava (Psidium guajava L.). India Biotechnol. 2010;9:176-195.
7. Gupta VK, Misra AK, Gaur RK, Jain PK, Gaur D, Sharma S. Current status of Fusarium wilt disease of guava (Psidium guajava L.). India Biotechnol. 2010;9:176-195.
8. Hussain MZ, Rahman MA, Bashar MA. Incidence of guava wilt (Psidium guajava) wilt caused by Fusarium sp. in Bangladesh. J Asiatic Soc Bangladesh. 2014;40(1):97-105.
9. Madhu MR, Verma KK, Kumar V. Distribution, prevalence and intensity of guava decline in western Haryana. J Entomol Zool. 2019;7(4):521-524.
10. Mamta J, Srivastava R, Sharma AK, Prakash A. Isolation and characterization of Fusarium oxysporum, a wilt-causing fungus, for its pathogenic and nonpathogenic nature in tomato (Solanum lycopersicum). J Appl Nat Sci. 2013;5(1):108-117.
11. Nikam PS, Jagtap GP, Sontakke PL. Survey, surveillance and cultural characteristics of chickpea wilt caused by Fusarium oxysporum f. sp. ciceri. Afr J Agric Res. 2011;6(7):1913-1917.
12. Pandey RR, Dwivedi RS. Fusarium oxysporum f. sp. psidii as a pathogen causing wilt of guava in Varanasi District, India. Phytopathol. 1985;2(114):243-248.
13. Patel N, Prasad N. Studies on Fusarium wilt of cumin. Plant Dis Reptr. 1964;47:528-531.
14. Yogeswari L. Trace element nutrition of fungi. The effect of boron, zinc and manganese on Fusarium species. Proc Indian Acad Sci. 1948;28:177-201.