Study on powdery mildew of cucumber caused by Erysiphe cichoracearum

Introduction

Powdery mildew-incited primarily by Golovinomyces cichoracearum (syn. Erysiphe cichoracearum)-stands out as an exceptionally destructive disease under both open-field conditions and protected farming structures. The fungus operates as an obligate parasite, initially establishing minute, white powdery patches on young foliage that rapidly expand to coat extensive surface areas of leaves and structural stems . This heavy mycelial covering triggers chlorophyll chlorosis, premature defoliation, and decreased photosynthetic capability. Consequently, yield losses ranging between 50% and 70% are frequently recorded when field environments favor early pathogenesis. Because powdery mildew development is highly sensitive to microclimatic elements like relative humidity and temperature variations, its structural severity remains deeply region-specific. Establishing effective management practices requires systematic field surveys to identify hotspot zones and map out regional disease intensity. While literature details its severity in regions like northern Karnataka or Uttar Pradesh, systematic survey data regarding southern Rajasthan's cucumber tracts remains scarce. Addressing this gap, this study systematically tracks, evaluates, and establishes the localized distribution, incidence, and severity of E. cichoracearum across major cucumber-producing pockets of southern Rajasthan.

Materials and Methods

Survey Design and Sampling Sites

An extensive roving field survey was completed during the 2024-25 crop seasons across the agricultural zones of southern Rajasthan. Three prominent cucumber-cultivating districts were chosen for evaluation: Udaipur, Chittaurgarh, and Banswara. To guarantee thorough regional representation and micro-climatic resolution, three distinct production blocks were systematically monitored in each target district: Udaipur District: Bargaon, Bhinder, and Girwa. Chittaurgarh District: Barisadri, Begun, and Bhadesar. Banswara District: Anandpuri, Arthuna, and Garhi. Observations were recorded at varying vegetative and reproductive crop growth stages across multiple farmer fields.

Assessment of Disease Incidence and Severity

Field disease incidence was mathematically calculated by counting the number of symptomatic, infected plants relative to the total plant population observed within designated sample plots. The assessment used the standard equation outlined by Wheeler (1969):

Disease Incidence (%) = 𝑁𝑜.𝑜𝑓 𝑖𝑛𝑓𝑒𝑐𝑡𝑒𝑑 𝑢𝑛𝑖𝑡𝑠 Total no.of units observed × 100

Disease severity profiles were calculated from randomly selected sample leaves using a modified 1-9 morphological rating scale as suggested by Naik and Kulkarni (2018) and Mayee and Datar (1986). The scale categorizes leaf area damage using the following visible diagnostic benchmarks

Data Analysis

The mean PDI values for individual tehsils and overall districts were aggregated and descriptive statistical comparisons were compiled using MS-Excel and basic analytical packages to interpret spatial variation against regional agro-climatic conditions.

Results

Field Diagnostics and Distribution

The field survey confirmed that powdery mildew is a highly prevalent disease across all monitored production pockets in southern Rajasthan. Symptoms were easily recognized by the presence of white to greyish talcum-like fungal growth on upper leaf surfaces, which gradually spread to lower leaf structures and stems as the plants aged. Severe infections frequently caused leaf chlorosis, drying, and premature defoliation.

District and Block-Level Analysis

The collected data revealed considerable variation in infection parameters across the surveyed regions (p. 28).

Overall, the combined mean field incidence stood at 48.65%, while the mean disease index was 40.85 PDI.

Udaipur Block-Level Dynamics (Low Baseline Zone)

Udaipur district showed the lowest baseline disease activity, recording a field incidence of 41.80% and a severity index of 34.60 PDI. At the micro-regional level, the Bargaon block recorded the lowest disease expression. This occurred as early-planted fields partially escaped peak spore dispersion. The Bhinder and Girwa blocks showed slightly higher values. In these blocks, lesions appeared primarily on older, lower leaves as isolated Grade 1 and Grade 3 specks before gradually moving upward into the younger plant canopy as ambient temperatures rose later in the season .The fact that overall disease incidence (48.65%) was higher than relative disease severity (40.85 PDI) indicates that while the pathogen successfully colonized a large percentage of cucumber plants, individual infection levels varied among fields.

Discussion

Conclusion

This systematic survey demonstrates that powdery mildew caused by Erysiphe cichoracearum is widely distributed and causes significant foliar damage to cucumber crops in southern Rajasthan. With an overall mean field incidence of 48.65% and a severity of 40.85 PDI, the disease presents a clear economic threat to local farmers. Block-level monitoring identified Banswara's Anandpuri and Garhi tracts as critical disease hotspots. These findings supply essential epidemiological data necessary for developing regional management strategies, timing protective fungicide applications, and introducing resistant cucumber cultivars to safeguard crop yields.

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