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Etiology and management of leaf spot disease of arecanut in northern Kerala By: Bhavana, A S
(Department of Plant Pathology, College of Agriculture, Padannakkad, 2026-02-19) Bhavana, A S; Sajeesh, P K
The study entitled “Etiology and management of leaf spot disease of
arecanut in Northern Kerala” was carried out in the Department of Plant
Pathology, College of Agriculture, Padannakkad during 2023-2025 with the
objective of etiology of the fungal pathogen/s associated with the leafspot disease
of arecanut and to formulate management strategies against the disease.
A purposive sampling survey was conducted in four AEUs of Kasaragod
and Kannur districts to collect infected and healthy leaf of arecanut leaf spot
disease affected palms samples. The fungi associated with the leaf spot
symptoms were isolated and characterised. Pathogenicity tests revealed that
twelve isolates were pathogenic, producing symptoms within 12–15 days after
inoculation. These twelve pathogenic isolates were subsequently sent to the Rajiv
Gandhi Centre for Biotechnology (RGCB), Thiruvananthapuram, for molecular
characterization. Among the six isolates three isolates showed high similarity
with Colletotrichum arecicola which is reported for the first time on arecanut in
India.
The contents of nitrogen (N), potassium (K), calcium (Ca), magnesium
(Mg), and boron (B) were analysed in both healthy and diseased leaf samples
collected from various locations and AEUs. A total set of healthy and diseased
leaf samples were analysed using standard protocols. It was found that K level
was consistently higher in healthy samples compared to diseased ones, indicating
the role of K in enhancing disease resistance. Nitrogen and magnesium showed
variable patterns depending on the AEU and did not follow a uniform trend.
Calcium content was generally higher in healthy leaves, except in the leaves
collected from AEU 13. Boron levels tended to be higher in diseased leaves
suggesting a possible stress induced accumulation.
Phylloplane microorganisms were isolated from the healthy arecanut
leaves. These were evaluated for antagonism towards Colletotrichum arecicola
using dual culture technique. Among them, two Trichoderma- like fungal
isolates and one-gram negative bacterial isolate exhibited strong inhibition of
the predominant pathogen C. arecicola. Under in vitro evaluation of fungicides
against C. arecicola by poison food technique, mancozeb (75WP) at 0.2%,
propiconazole (25EC) at 0.2% and carbendazim 12% + mancozeb 63% (75
WP) at 0.2% exhibited high inhibition (100%). These three fungicides, along
with the antagonists selected from phylloplane used for in vivo evaluation
against the disease. Fungicides and antagonists were applied one week after
pathogen inoculation on leaves. After 15 days of fungicide application,
propiconazole (25 EC) at 0.2% and carbendazim 12% + mancozeb 63% (75
WP) at 0.2% were found effective against arecanut leaf spot.
The study identified as C. arecicola is the major cause of arecanut leaf
spot in Northern Kerala, and it reported for the first time on arecanut in India.
Nutrient analysis showed that higher potassium levels were associated with
healthier leaves. Among the management options tested, propiconazole (25 EC)
at 0.2% and carbendazim 12% + mancozeb 63% (75 WP) at 0.2% were the most
effective in reducing disease severity. The findings are helped to learn more
about the etiology of the leaf spot disease and in developing improved fungicide
and fertilizer schedules for managing arecanut leaf spot disease.
Characterization of pathogens causing canker and dieback diseases in moringa (Moringa oleifera Lam.)
(Department of Plant Pathology, College of Agriculture, Vellanikkara, 2026-02-06) Adithya Sreekumar; Anju, C
Canker and dieback are increasingly recognized as major constraints in moringa
cultivation, despite the crop’s well-known resilience and rich phytochemical defence.
Field observations across Kerala have indicated a rising incidence of these diseases
affecting young and mature plants alike, yet systematic documentation of the causal
pathogens and their interaction with the host remains limited. The present investigation
was undertaken to identify, characterize and evaluate the pathogenic potential of fungi
associated with canker and dieback diseases of moringa, and further to assess host
biochemical responses at critical developmental stages. The study was carried out in the
Department of Plant Pathology, College of Agriculture, Vellanikkara, from 2023 to
2025.
A purposive survey of moringa-growing homesteads and nurseries in Thrissur
(AEU 10) and Ernakulam (AEU 12) districts yielded a total of 65 diseased samples
from which 77 fungal isolates were obtained, comprising 50 from canker-affected
tissues and 27 from dieback samples. Disease intensity varied among locations, with
the highest PD1 for canker recorded at Kolazhy (AEU 10) (89.28 %), while the
maximum PD1 for dieback was recorded at Kothamangalam (AEU 12) (76 %). Several
samples yielded multiple isolates, indicating the coexistence of distinct fungal species
within the same lesion. Isolates were purified using hyphal-tip culture and maintained
on PDA for further studies. Canker symptoms under natural conditions included
superficial bark cracking, pale-yellow to light-brown sunken or flat lesions and
localized necrosis. Dieback symptoms, on the other hand, were characterized by
progressive twig/branch drying, extensive cortical discoloration and the appearance of
black, pinhead-like pycnidial structures on severely affected tissues. Pathogenicity
testing conducted under rain-shelter conditions confirmed the ability of all tested
isolates to reproduce disease symptoms on moringa, fulfilling Koch’s postulates.
Symptom development varied markedly among isolates, indicating a wide spectrum of
virulence.
Cultural and morphological characterization of the isolates revealed
considerable diversity in colony growth, pigmentation, sporulation and microscopic
traits. Isolates associated with canker generally produced fast-spreading, cottony to
fluffy mycelium with pink, white, or grey colouration, while dieback-associated isolates
commonly showed dark, melanised mycelium with abundant pycnidial formation.
Molecular characterization using ITS, TEF-1α and RPB2 gene regions confirmed the
presence of multiple pathogenic species on moringa. Canker symptoms were associated
with Fusarium irregulare, F. citri, Nectria sp. and Lasiodiplodia theobromae, whereas
dieback was predominantly caused by L. theobromae, Curvularia sp. and Diaporthe
batatas. This represents the first comprehensive documentation of the canker-dieback
pathogen complex occurring on moringa in Kerala.
Extracellular cellulases and pectinases production was evaluated using
substrate-amended media. All isolates exhibited measurable cellulolytic and
pectinolytic activity. Among the 77 tested isolates, several, including Fusarium sp.
(AIS5), Fusarium sp. (VLD2), Lasiodiplodia sp. (VLD1), Fusarium sp. (MAD),
Curvularia sp. (MLD2) and Curvularia sp. (AVD3), produced large hydrolytic zones
(mm) within just 2-3 days, reflecting a strong enzymatic activity. Statistical analysis
2
revealed a highly significant positive correlation between lesion size and enzyme
activity, indicating that both cellulase and pectinase secretion are strongly linked to
virulence expression.
Two highly virulent isolates, L. theobromae, CHS2 (canker) and L. theobromae,
TRD1 (dieback), were selected for biochemical assays. Host response was examined at
five principal developmental stages: leaf, shoot, flowering, fruiting and senescence.
CHS2 produced small, slowly enlarging lesions across all developmental stages,
beginning as light-brown or pale-yellow spots (0.1-0.2 cm) that expanded slowly and
developed into ovoid to spindle-shaped forms with mild cracking by day five. In
contrast, TRD1 generated faster-expanding lesions even in early stages, initial pale
brown patches (0.1-0.2 cm) rapidly enlarged (up to 2.5 cm by day 5) and frequently
coalesced, progressing from pale yellow or water-soaked patches to darker brown or
black lesions. Overall, CHS2 showed slower, stage-dependent lesion expansion,
whereas TRD1 exhibited rapid, aggressive lesion development across all growth stages.
Total phenolic content varied widely among growth stages and according to
pathogens. In the flower development stage, inoculated plants accumulated
substantially higher phenols than controls from one day after pathogen inoculation,
indicating a pronounced early defence response. Conversely, in leaf and fruit
development stages, phenol levels in inoculated plants dropped significantly below
those of the corresponding controls, suggesting growth stage-specific phenol
biosynthesis in response to pathogen infection. During senescence, phenol levels
remained low across TRD1 inoculated treatment, reflecting a natural decline in defence
capacity. Flavonoid content showed a transient decline at one to two days post
inoculation across most developmental stages. This was followed by a clear rebound on
days three and five, especially in the leaf and shoot development stages, reflecting
induced defence activation. In the leaf development stage inoculated with CHS2,
flavonoids increased markedly by day five (22.85 mg QE g⁻¹; ~26% above control).
TRD1-inoculated tissues displayed a similar pattern of early reduction followed by
strong accumulation of flavonoids from day three.
Overall, the study establishes that canker and dieback in moringa are caused by
a diverse assemblage of fungal pathogens exhibiting wide variability in virulence and
extracellular enzyme activity. The findings highlight the central role of cell-wall
degrading enzymes in facilitating tissue colonization and disease progression.
Moreover, phenolic and flavonoid profiling across growth stages reveals that moringa
exhibits a highly stage-dependent defence strategy, with stronger biochemical activation
during early vegetative growth and flowering stages and weaker responses during
fruiting and senescence. These insights form an essential foundation for developing
stage-specific disease management strategies and for future exploration of host
resistance mechanisms in moringa.
Host plant resistance in cowpea (vigna unguiculata (L.) Walp) against Aphis craccivora Koch (Hemiptera: Aphididae)
(Department of Entomology, College of Agriculture, Padannakkad, 2026-02-16) Aiswarya Mohan, S; Thania Sara Varghese
The present study titled ‘Host plant resistance in cowpea (Vigna unguiculata (L.)
Walp) against Aphis craccivora Koch (Hemiptera: Aphididae)’ aimed to assess the
resistance or susceptibility of cowpea germplasms to A. craccivora and to identify the
mechanisms underlying this resistance through antixenosis, antibiosis and biochemical
analyses. Field screening of thirty-two cowpea germplasms was conducted from
January to March 2025 at Instructional Farm I, College of Agriculture, Padannakkad,
under natural infestation conditions.
In the field evaluation, Kashi Nidhi (13.27) recorded highest number of aphids
per 2.5 cm shoot and Kashi Gauri the lowest (0.15). Other insect pests such as stem fly,
leaf miner, leaf roller and cow bug were also observed, though significant differences
were noted only in stem fly and leaf miner incidence. Stem fly damage was highest in
Lola (6.33) and lowest in Konkan Wali (0.00), while leaf miner incidence was greatest
in TCR 57 (1.13) and lowest in Lola, KAU Sreenandha, TCR 53, TCR 36 and
Maharashtra local variety 3(0.00). Despite these variations, no visible foliar or floral
damage attributable to aphids was recorded, and population differences alone were
insufficient to categorise the entries into resistant/ susceptible under field conditions.
In that context, cage screening was conducted that provided a clearer separation
of germplasm response to A. craccivora. Seedling survival after release of aphids was
found to be highest in Arka Samrudhi (41.67) and lowest in Geethika, Karkoonthal
Payar and Maharashtra Local variety 3 (15). Damage assessments showed a comparable
pattern, with Geethika, Karkoonthal payar and Maharashtra local variety 3 recording
the highest cumulative scores (5.00) and Arka Samrudhi (2.11) the lowest. None of the
germplasms were categorized as highly resistant or resistant; five were classified as
moderately resistant (MR), nine as moderately susceptible (MS), and eighteen as highly
susceptible (HS). Two germplasms from each category - MR (Anaswara, Arka
Samrudhi), MS (Konkan Wali, Phule Pandhari), and HS (Geethika, Karkoonthal payar)
were selected for studying host plant resistance mechanisms.
Antixenosis (non-preference) studies on the six selected germplasms revealed
that mean number of aphids migrated per plant was highest in highly susceptible
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Geethika (90.50) and lowest in moderately resistant Arka Samrudhi (23.25). The
selected germplams showed an effect on growth, reproduction and survival of the
aphids. The mean weight of 10 aphids and number of progeny per aphid were maximum
in Geethika (7.32 mg and 21.00, respectively) and the mean survival period was highest
in Karkoonthal payar (10.25 days), whereas Arka Samrudhi recorded the lowest values
for all three parameters (4.68 mg, 6.75 progeny, and 6.75 days, respectively). The results
indicate that highly susceptible genotypes promote aphid development and survival
whereas moderately resistant types suppress growth, reproduction and longevity.
Biochemical and nutrient estimation of the selected MR and HS germplasms
showed that nitrogen, phosphorus, potassium and protein contents were highest in
Karkoonthal payar (5.45%, 0.48%, 4.72% and 340468.75 µg g⁻¹ respectively) and
lowest in Arka Samrudhi (3.35%, 0.24%, 2.66%, 209531.25 µg g⁻¹respectively). The
total phenol content was highest in Anaswara (381.56 µg g-1) and lowest in Geethika
(186.21µg g-1), and both flavonoid and terpenoid levels were highest in Arka Samrudhi
(1326.26 µg g-1, 4775.83 µg g-1) and lowest in Karkoonthal payar (496.43 µg g-1,
2309.24 µg g-1).
The highly susceptible Geethika showed maximum plant height (142.80 cm) and
number of primary branches (7.75), while moderately susceptible Phule Pandhari
(29.15 and 3.00 respectively) recorded the lowest values. Number of leaves/plant were
highest in Anaswara (17.75) and lowest in Phule Pandhari (9.25). Trichome density
was greatest in Karkoonthal payar (21.50/cm leaf margin) and lowest in Anaswara
(14.75/cm leaf margin), whereas trichome length was longest in Anaswara (0.42 mm)
and shortest in Karkoonthal payar (0.10 mm).
In the present study, principal component analysis clearly separated resistant and
susceptible germplasms, with Arka Samrudhi and Anaswara clustering opposite
Geethika and Karkoonthal payar, showing that resistance was associated with higher
biochemical defenses and longer trichomes, whereas susceptibility clustered with
elevated nutrient levels and stronger aphid performance traits.
Genetic diversity analysis and in vitro seedling production of mangosteen (Garcinia mangostana L.) accessions
(Department of Fruit Science, College of Agriculture, Vellayani, 2026-02-09) Harsha, K S; Simi, S
The study entitled “Genetic diversity analysis and in vitro seedling production of
mangosteen (Garcinia mangostana L.) accessions” was conducted at the Department of
Fruit Science and the Department of Molecular Biology and Biotechnology, College of
Agriculture, Vellayani, during the period 2023–2025. The investigation aimed to assess the
genetic diversity of mangosteen accessions using molecular markers and in vitro seedling
production to enhance seedling vigour.
Thirty mangosteen genotypes cultivated in Thrissur and Wayanad districts of
Kerala were subjected to molecular characterization. Genomic DNA was isolated from
young leaves using the CTAB extraction method (Doyle and Doyle, 1987) with
modifications
proposed
by
Sulassih
and
Santosa
(2020)
incorporating
polyvinylpyrrolidone (PVP) to eliminate polyphenolic impurities. The DNA samples
showed UV absorbance ratios (A260/A280) between 1.79 and 2.07 indicating their purity.
Ten Inter Simple Sequence Repeat (ISSR) primers, previously reported in
mangosteen, were used for amplification. These primers produced a total of 71 loci across
the thirty genotypes of which 63 were polymorphic resulting in a mean polymorphism
percentage of 85.87%. The number of loci per primer varied from 3 (UBC 860) TO 11
(UBC 840) indicating considerable variation in amplification efficiency. The Polymorphic
Information Content (PIC) values ranged between 0.04 (UBC 860) and 0.39 (UBC 825)
with an average of 0.28, indicating moderate informativeness. Cluster analysis using the
Unweighted Pair Group Method with Arithmetic Mean (UPGMA) based on Jaccard’s
similarity coefficients revealed three major clusters at a similarity coefficient of 0.66
corresponding to 34% dissimilarity. Cluster I comprised a single accession (Acc. 017) that
was distinctly separated indicating a high degree of divergence. Cluster II containing
twenty six accessions was further divided into subclusters II A and II B at 0.68 similarity,
while Cluster III included three accessions (Acc.004, Acc.048, and Acc.126). Principal
Coordinate Analysis (PCA) further supported the clustering pattern, indicating the
moderate genetic differentiation among the genotypes.
Investigations were also carried out for in vitro seedling production of mangosteen.
Mature seeds of mangosteen were aseptically cultured on Murashige and Skoog (MS) and
85
half-strength MS media containing different concentrations of sucrose (1%, 2%, and 3%)
and gibberellic acid (GA₃) (0, 0.2, 0.5, and 1 ppm). Twelve treatment combinations were
evaluated for their influence on germination, subsequent seedling vigour and growth.
Significant variation was observed among treatments for all parameters studied.
The mean number of days required for germination ranged from 12.33 to 22.67 days. The
earliest germination was observed in treatment T₁₂ (½ MS + 2% sucrose + GA₃ 1 ppm).
Similarly the germination percentage also varied significantly, with T₁₂ showing the highest
value (95.24%) followed by T₁₀ (½ MS + 2% sucrose + GA₃ 0.2 ppm). Seedling vigour
indices (SVI-I and SVI-II) reflected a similar trend with T₁₂ recording the highest values
(1383.81 and 44.48, respectively), indicating the positive influence of reduced salt
concentration and GA₃ supplementation on germination and early growth.
Growth parameters recorded at the time of plant out revealed significant differences
among treatments. The longest shoots (5.73 cm), roots (3.87 cm) and leaves (4.77 cm) were
recorded in T₁₂. After four weeks of hardening, seedlings from T₁₂ maintained superior
performance with the highest shoot length (7.10 cm), root length (7.17 cm), and leaf length
(6.17 cm). The number of leaves was the highest in T₈ (MS + 2% sucrose + GA₃ 0.5 ppm)
and T12 (½ MS Media (2% sucrose) + GA 1 ppm). Survival percentage did not differ
significantly among treatments; however, T₁₂ and T₆ recorded the highest survival
percentage (95.24), indicating the robustness of the developed seedlings. These results
demonstrated that half-strength MS medium supplemented with 2% sucrose and 1 ppm
GA₃ was optimal for inducing early germination, improving root and shoot elongation, and
enhancing seedling vigour.
The present study confirms the existence of genetic diversity among
mangosteen accessions in Kerala despite their apomictic nature. The moderate
polymorphism revealed by ISSR markers indicates underlying genetic differentiation
likely resulting from somatic mutations or environmental adaptation. The optimized in
vitro germination media (½ MS medium supplemented with 2% sucrose and 1 ppm GA₃)
proved effective in enhancing germination, seedling vigour, and survival percentage.
Production technology and post harvest handling techniques of orange jasmine (Murraya paniculata (L.)Jack)
(Department of Floriculture and Landscaping, College of Agriculture, Vellanikkara, 2026-01-09) Nandana Bhaskaran; Simmy, A M
Orange jasmine (Murraya paniculata (L.) Jack) is a tropical ornamental shrub
belonging to the Rutaceae family, native to South and Southeast Asia, valued for its
glossy foliage and aesthetic appeal in floral arrangements. The plant has gained
commercial importance in the cut foliage industry, particularly in Kerala's favourable
humid tropical climate. Despite its growing demand, the crop faces significant
challenges due to non standardised agronomic practices and inadequate post-harvest
handling techniques, resulting in reduced productivity and limited vase life, leading to
substantial economic losses. The present study, entitled 'Production technology and
post-harvest handling techniques of orange jasmine [Murraya paniculata (L.) Jack] was
carried out at the Department of Floriculture and Landscaping, College of Agriculture,
Vellanikkara, Thrissur, during 2024-2025 to standardise spacing, nutrient management
protocols, and post-harvest handling techniques for commercial cultivation and vase
life enhancement of orange jasmine foliage.
The first experiment evaluated the effects of three plant spacings (1 m × 1 m, 1.5
m × 1.5 m, and 2 m × 2 m) and three nutrient doses (75:8:15, 100:8:15, and 50:8:15
N:P₂O₅:K₂O g/plant/year) on growth and yield parameters. Plant height was
significantly affected by nutrient application; the 75:8:15 and 100:8:15 N:P₂O₅:K₂O
treatments resulted in maximum heights of 127.66 cm and 126.55 cm respectively. The
widest spacing (2 m × 2 m) combined with the highest nutrient dose produced the largest
number of harvestable shoots (6.33 shoots). The greatest yield (5.49 t/ha) was observed
at the closest spacing (1 m × 1 m), while the 100:8:15 N:P₂O₅:K₂O dose yielded 4.65
t/ha, and their combination resulted in the highest overall yield of 7.89 t/ha. The 2 m ×
2 m and 100:8:15 N:P₂O₅:K₂O combination led to the heaviest shoots (159.39 g) and
the shortest duration to first harvest (278.33 days). Maximum chlorophyll content (1.25
mg/g FW) was recorded at the 1 m × 1 m spacing, and 1.18 mg/g FW at the highest
nutrient dose. The lowest nutrient dose N3(50:8:15 N:P₂O₅:K₂O) resulted in the longest
vase life (13.33 days)
The second set of experiments standardised post-harvest techniques through four
sequential studies. Precooling treatments showed that the untreated control recorded the
longest vase life of 13.26 days. Pulsing with BA 50 ppm extended vase life to 17.44
days, followed by BA 25 ppm (14.78 days), while the sucrose combinations reduced
vase life. Packaging and storage experiments showed that polypropylene sleeves (P₄)
and newspaper cover (P₇) with a 48-hour storage duration yielded optimal results. The
combination of polyethylene sleeve with KMnO₄ sachet stored for 48 hours (P₃ × S₂)
achieved the maximum vase life of 25.67 days. Holding solution experiments
demonstrated that sodium benzoate treatments were most effective, with concentrations
of 50 ppm and 100 ppm, extending vase life to 14.83 and 14.33 days, respectively.
The present study demonstrated that the combination of optimal spacing (1 m × 1
m), and the highest nutrient dose (100:8:15 N:P₂O₅:K₂O g/plant/year) produced the
highest yield proving that these treatments are best suitable for the cultivation of
Murraya paniculata. For the post-harvest practices, omitting precooling, pulsing cut
shoots with 50 ppm BA for 6 hours, packaging in polyethylene sleeve with KMnO₄
sachet for 48 hours, and using sodium benzoate as a holding solution maximized vase
life. This research provides a comprehensive production and post-harvest management
protocol to enhance commercial viability and promote a sustainable supply chain for
the orange jasmine cut foliage industry in Kerala.