Role of plant growth promoting microbes in the control of fungal foliar diseases of tomato under protected cultivation – Egyptian Journal of Biological Pest Control

Early blight

During Kharif 2017–2018 (Table 1), the disease incidence treated with T3 and T7 was recorded as 14.80 and 16.28%, respectively, compared to other treatments. After the third spray, the disease incidences at T2 (19.24%), T3 (19.98%), followed by T5 (28.86%), T6 (27.38%), and T7 (25.16%) were found to be significantly (p < 0.05) lower than the T8 (40.70%) against early blight. During Kharif 2018–2019 (Table 2), the incidence after the first spray was found to be ranged from 21.18% (T4) to 26.19% (T8). After the second spray, the diseases in T2 (24.10%), T3 (25.16%), and T4 (23.40%) were comparatively lower than the untreated control T8 (36.30%). After three times spray, T2 (22.10%), T3 (24.10%), T4 (27.31%), T5 (28.10%), and T6 (27.33%), the disease incidence was found significantly (p < 0.05) lower or at par with each other than the untreated control T8 (48.45%). At the end of the fourth spray, the most negligible early blight incidence was recorded in the treatments T2 (22.31%), T3 (22.60%), T5 (25.13%), and T6 (26.15%), and the highest was in untreated control T8 (53.15%).

Powdery mildew

During the Kharif 2017–2018 (Table 1), the low disease incidences ranged from 15.54 to 24.42% in all the treatments except in T1 (27.38%) and T7 (26.29%), compared to T8 (29.60%), which were assessed only after the fourth spray. The disease incidences during Kharif 2018–2019 (Table 2), T2 (12.10%), and T3 (13.19%) treatments were compared and statistically superior vis-à-vis untreated control T8 (23.61%).

Septoria leaf spot

The disease incidence during the Kharif 2017–2018 (Table 1), the septoria leafspot incidences ranged from 13.32% (T2) to 14.80% (T8) after the third spray. The lowest septoria leaf spot diseases were recorded in the T2 (23.16%), T3 (26.40%), T5 (24.78%), and T6 (24.12%), compared to control (41.42%) during the Kharif, 2018–2019. The pooled data of both the years also showed that the early blight incidences were significantly lower (p < 0.05) in T2 (21.41%) and T3 (20.66%), and the powdery mildew incidences in T2 (13.82%) and T3 (15.48%) and septoria leaf spot incidences in T2 (19.35%) and T3 (22.08%) had also followed similar trend.

The biocontrol agents viz., T. harzianum and B. subtilis had shown positive results for the production of HCN by changing the colour of filter paper that was pre-added with picric acid from light yellow to orange (Fig. 1a). P. fluorescens tested negative for the HCN production as it didn’t change the colour of filter paper from yellow to orange. P. fluorescens and B. subtilis produced yellow halos around the colony confirming the siderophore production (Fig. 1b). T. harzianum showed a negative result for the siderophore production as it did not produce yellow halos around the mycelial growth in the CAS (Chrome Azurol S) media. T. harzianum was found to be positive for the test. It was observed by a change in media colour from pinkish-red to purple. P. fluorescens and B. subtilis have shown negative for the chitinase test as the colour of the media did not change (Fig. 1c).

a–c Characterization of antagonistic microorganisms for the production of HCN, Siderophore and Chitinase by Trichoderma harzianum, Pseudomonas fluorescens and Bacillus subtilis

Plant height (Fig. 2)

Pooled analysis of various treatments and their influence on plant parameters (Kharif 2017–2018 and 2018–2019). As compared to control T8, all the treatments have significant impact (p < 0.05) on the plant parameters (plant height, number of fruits per cluster and number of pickings). This figure shows that as compare to other treatments, plant parameters are comparatively higher (p < 0.05) with the treatment T3 and provided a maximum yield followed by the treatments T2, T5 and T6

The plant height varied between 20.3 and 35.7 cm. The maximum height was recorded in T3 (35.7 cm), which was found on par with 32.7 cm (T4), followed by T2 (31.7 cm), T5 (32.0 cm), and T6 (30.0 cm), and the minimum height was recorded in T8 (20.3 cm).

Fruits per cluster (Fig. 2)

The highest numbered of fruits per cluster were recorded in T3 (6.33) and T2 (5.67), followed by T4 (5.00), T5 (5.33), and T6 (4.33), and the lowest in the T8 (2.33).

Several pickings (Fig. 2)

The maximum pickings were recorded in T3 (12.00), T4 (11.67), T2 (11.33), and T5 (11.33). The minimum pickings were recorded in T8 (7.33).

Yield

During Kharif 2017–2018, the pooled mean values ranged from 43.13 t ha⁻¹ to 61.57 t ha⁻¹ (Table 1). The highest was in the T2 (60.05 t ha⁻¹), T3 (61.57 t ha⁻¹), and T6 (59.47 t ha⁻¹), and the lowest in T8 (43.13 t ha⁻¹). A similar trend was recorded during the subsequent year, Kharif 2018–2019 (Table 2), with the highest yields in T2 (58.61 t ha⁻¹), T3 (57. t ha⁻¹), followed by T6 (54.34 t ha⁻¹), and T7 (51.10 t ha⁻¹) and the lowest in untreated control T8 (39.22 t ha⁻¹). The pooled analysis of the yield data also revealed that the maximum yields were recorded in T2 (58.93 t ha⁻¹) and T3 (59.92 t ha⁻¹), followed by T5 (55.07 t ha⁻¹) and T6 (56.41 t ha⁻¹) and the minimum in yield in untreated control T8 (40.68 t ha⁻¹).

Cost–benefit ratio (Fig. 3)

Cost economics of management of fungal foliar diseases of tomato in a polyhouse condition (T1-Seed treatment, seedling dip and spray with T. harzianum; T2-Seed treatment, seedling dip and spray with B. subtilis; T3-Seed treatment, seedling dip and spray with P. fluorescens; T4-Seed treatment and spray with T. harzianum; T5-Seed treatment with T. harzianum and spray with B. subtilis; T6-Seed treatment with T. harzianum and spray with P.fluorescens; T7-Spray with Sulphur and T8-Untreated control)

The cost of cultivation in all the treatments ranged from Rs. 2, 60,000 ha⁻¹ (T8) to a maximum of Rs. 2, 78,960 ha⁻¹ (T3). The maximum gross return was obtained in T3 (Rs. 8, 98,800 ha⁻¹), followed by T2 (Rs.8, 83,950 ha⁻¹) and the minimum in T8 (Rs.6, 10,200 ha⁻¹). The highest net returns were recorded in T3 (Rs. 6, 19,840 ha⁻¹) and T2 (Rs. 6, 06,250 ha⁻¹) and the lowest in T8 (Rs. 3, 50, 200 ha⁻¹). The highest benefit: cost ratios of 3.22:1 and 3.18:1 were obtained in T3 and T2 and the lowest was in T8 (2.34:1).