PhD

Spent mushroom substrate (SMS) is the composted organic material
retained after a crop of mushroom. The world mushroom industry needs to discard
more than 50 million tons of SMS every year. The latest research throw light on
the efficient use of SMS for the disease management of crop plants.
A
preliminary study on the use of SMS of Pleurotus spp. as mulch for the
management of rhizome rot complex disease of ginger under pot culture condition
was carried out in the Department of Plant Pathology, College of Horticulture,
Vellanikkara. In this study, among the various SMS used, the paddy straw SMS of
P. sajor-caju as mulch recorded the highest biometric characters and least disease
incidence compared to control. Hence this project was proposed as the
continuation of the above study to evaluate the efficacy of enriched SMS of
P. sajor-caju in enhancing growth and systemic resistance for the management of
soil borne pathogens of ginger under field conditions.
SMS of P. sajor-caju was produced during three different periods viz.,
March-April, June-July and November-December (2013) at six different locations
of Kerala viz., College of Horticulture, Vellanikkara (Thrissur dist.), farmer’s field
at Kodakara (Thrissur dist.), Perinjanam (Thrissur dist.), Krishnagiri (Wayanad
dist.), Mananthavady (Wayanad dist.) and College of Agriculture, Vellayani
(Thiruvananthapuram dist.). Enumeration of microflora of these SMS was carried
out and a total of 47 fungal and 45 bacterial isolates were obtained. The
antagonistic efficiency of these isolates were evaluated against the five pathogens
viz., Pythium aphanidermatum, Fusarium oxysporum, Rhizoctonia solani,
Sclerotium rolfsii and Ralstonia solanacearum under in vitro conditions. All the
isolates from SMS showed antagonistic property against one or the other soil
borne pathogens, with varying degree of inhibition. Mutual compatibility between
the most efficient fungal and bacterial antagonists was evaluated to develop an
effective microbial consortium for enriching the SMS and could be used against
the soil borne diseases of ginger.
Biosoftening efficiency of selected fungal and bacterial antagonists on
SMS was evaluated. Two separate experiments were carried out with the selected
antagonists effective against fungal and bacterial pathogens. For each experiment,
five fungal antagonists, five bacterial antagonists and three compatible pairs were
selected based on the in vitro evaluation of antagonistic efficiency and mutual
compatibility studies. SMS was enriched separately with different antagonists and
standardized the period for biosoftening of SMS as mulch for ginger cultivation.
A period of 15 days was selected as most suitable for biosoftening the SMS as
mulch with optimum antagonistic fungal and bacterial population. Wide range of
C:N ratio was recorded by the SMS enriched with each antagonists. By
considering the C:N ratio along with external appearance, the treatments having
C:N ratio of 30:1 to 45:1 were selected, since it was the most suitable stage to be
used as mulch in ginger.
The effectiveness of biosoftened SMS against rhizome rot and bacterial
wilt diseases of ginger was evaluated in two pot culture experiments. Three fungal
and bacterial antagonists each and one compatible pair of antagonists which were
selected based on the in vitro evaluation of antagonistic and biosoftening property
were used for enriching the SMS. After enrichment, the SMS were kept for 15
days for biosoftening and were applied as mulch in the experiments. Observations
on germination percentage and other growth parameters viz., number of
tillers/plant, number of leaves/tiller and height of tillers were recorded at one
month intervals from two months after planting (MAP). Challenge inoculation of
pathogens was done at 45 days after germination and per cent disease incidence
was recorded at 7 and 14 days after inoculation (DAI).
In the experiment for the management of P. aphanidermatum, the lowest
disease incidence was observed in T7 (SMS softened with P1F1+ M1F2) on 14th day
after inoculation (DAI). This treatment also recorded the highest number of tillers,
number of leaves/ tiller and height of tillers and rhizome yield. In the experiment
for the management of R. solanacearum, the treatment T2 (SMS softened with
T1F2) was found to be the most efficient one, which recorded the least disease
incidence at 14 DAI, whereas the highest values for biometric characters and
rhizome yield were recorded by T7 (SMS softened with K1B1 + T2B1).
The activity of phenol and defense related enzymes such as peroxidase
(PO), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were
estimated by spectroscopy, before challenge inoculation with pathogen and at one,
three and five days after the challenge inoculation. For estimation, leaf samples
were collected separately from the pot culture experiments I and II for the
management of P. aphanidermatum and R. solanacearum respectively. The
treatments which recorded less disease incidence in both the pot culture
experiments exhibited the highest activity of defense related enzymes and phenol.
The highest activity of defense related enzymes and phenol was recorded at 5
DAI. Thus the present study showed that in addition to direct antagonism and
plant growth promotion, induction of defense related enzymes was also
contributed by SMS to enhance resistance against invasion of soil borne
pathogens of ginger.
Field evaluation of the selected treatments from pot culture experiments
showed the lowest disease incidence in the treatment T2 (SMS softened with T1F2)
followed by T5 (SMS softened with P1F1+M1F2). Statistically these were on par
with each other. The treatment T5 (SMS softened with P1F1+M1F2) recorded the
highest germination percentage, number of tillers, number of leaves/tiller and
rhizome yield also. Analysis of primary nutrients viz., nitrogen, phosphorus and
potassium in SMS, plant and soil from field experiment was conducted. Among
these, SMS softened with P1F1+M1F2 recorded the highest percentage of N, P and
K. This treatment recorded the highest nutrient content in ginger rhizome and soil
also.
Attempts were also made to identify the fungal and bacterial antagonists
selected for field experiment. Based on the cultural and morphological characters,
the fungal antagonists viz., Kr1F4, T1F2, P1F1 and M1F2 were tentatively identified
as Trichoderma viride (Pers.), T. viride (Pers.), T. koningii (Oudem.) and T.
harzianum (Rifai) respectively. The identification got confirmed from National
Centre for Fungal Taxonomy (NCFT), New Delhi. The bacterial antagonists
selected for field experiment were also identified based on cultural,
morphological, biochemical and 16s rRNA sequence analysis. The three bacterial
antagonists P3B2, T2B1 and K1B1 were identified as Bacillus safensis, B.
methylotrophicus and Burkholderia gladioli respectively.
Spent mushroom substrate is rich in microflora and these microflora exert
antagonistic activities against soil borne pathogens. It stimulates the natural
defense system in plants, provide necessary nutrients for plant growth and also
improve soil physical condition. From field evaluation it was found that the SMS
softened with T. viride recorded the lowest disease incidence and which enhanced
systemic resistance to soil borne pathogens of ginger by defense related enzymes
and phenol. The results were on par with the SMS softened with consortium of
antagonists, T. koningii and T. harzianum (P1F1+M1F2). The highest rhizome yield
and other growth parameters were also contributed by the SMS softened with T.
koningii and T. harzianum. The content of nitrogen, phosphorus and potassium
were also recorded the highest in this SMS. So from the present study it can be
concluded that the SMS softened with T. koningii and T. harzianum can be used
as mulch in ginger which was found equally effective to induce systemic
resistance against soil borne pathogens and to enhance growth parameters and
rhizome yield.