THE BIOLOGY AND CONTROL OF CONIELLA LEAF SPOT OF KENAF, HIBISCUS CANNABINUS L., INDUCED BY CONIELLA MUSAIAENSIS B. SUTTON VAR HIBISCI B. SUTTON
THE BIOLOGY AND CONTROL OF CONIELLA LEAF SPOT OF KENAF, HIBISCUS CANNABINUS L., INDUCED BY CONIELLA MUSAIAENSIS B. SUTTON VAR HIBISCI B. SUTTON
No Thumbnail Available
Date
1991-10
Authors
ADEPOJU, AREMU ADEOTI
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Symptomatological studies and pathogenicity tests confirmed
that the Coniella leaf spot of kenaf observed in Mokwa in Nigeria
was induced by Coniella musaiaensis B. Sutton var hibisci B.Sutton
(IMI NO. 280998 and 2809996). Field survey conducted in the
southern Guinea savanna of Nigeria in 1984 indicated that C. musaiaensis
induced between 41,5 and 98.2 percent damage to the leaves. Out of
57 kenaf cultivars screened on the field and glasshouse for resistance
to the pathogen, only Tianung No.lwas free of the disease, three other
cultivars, AMC 108 kenaf, A60-282 and local line 1 exhibited high
resistance.
The month of May at Mokwa, in the southern Guinea savanna, was
the best for planting kenaf to avoid severe disease attack and to
obtain high grain and fibre yields Planting as from July resulted
in flowering in August(when the day length has fallen), severe
attack by the leaf spot disease and low grain and fibre yields.
Application of NPK fertilizer increased kenaf growth and fibre
yield but increased Coniella leaf spot severity on the crop. Supply
of N as sole fertilizer also predisposed kenaf plants to attack by
the leaf spot. In both cases, the age of plant at first apprearance
of disease symptom was reduced significantly (P = 0.05) when
compared with plots where NP and NK fertilizers were used. Supply of
NP or NK fertilizers significantly (P = 0.05) delayed the time of
disease attack on kenaf, reduced disease severity and increased both
grain and fibre yields.
In-vitro assessment of four fungicides showed that carbendazim
andbenemy1 completely inhibited the mycelial growth of the fungus
in agar medium at the commercial dosage and at lower concentrations
tested. Calixin M and Mancozeb inhibited mycelial growth in culture
only at double the commercial dosage. The four fungicides significantly
(P = 0.05) reduced the disease severity when sprayed at twoweekly
interval compared with the check that was sprayed with water.
There was no significant difference (P = 0.05) in disease severity
between kenaf plants sprayed with carbendazim at 7-day and 14-day
intervals. There were also no significant differences (P = 0.05)
in disease severity when the four fungicides were sprayed at 21—and
28-day intervals when compared with the controls in the two years.
Retted fibres from fungicide-treated plots showed that there was no
need to spray for Coniella leaf spot control if the ultimate aim of
planting kenaf was fibre production, because the check plots gave
fibre yields comparable in weight with the sprayed plots. However,
it is necessary to spray the plots if grain production is required
since the fungicide-treated plots gave significantly (P = 0.05)
higher grain yield than the unsprayed plots.
Out of the 17 plant species belonging to 9 taxonomic families
tested for susceptibility to C. musaiaensis, five species - okra,
Abelmeschus esculoentus L.; cotton, Gessypium hirsitum L.; pepper,
Capsicum annun L.; and two cultivars of reselle (Hibiscus sabdariffa)
were found to be susceptible. H. sabdariffa has been reported earlier
as an alternative host of the pathogen while the other plants are
being reported for the first time.
Based on the interaction in the glasshouse between 9 selected
kenaf cultivars (3 resistant, 3 moderately resistant and 3 susceptible)
as host differentials and 51 isolates of C. musaiaensis collected from
many kenaf growing areas in the southern and northern Guinea savanna
zones of Nigeria, six pathogenio groups of the organism were proposed.
The immediate implication of this is is that more races of the
pathogen are probably existing in Nigeria.
Description
A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY IN CROP PROTECTION
DEPARTMENT OF CROP PROTECTION
FACULTY OF AGRICULTURE
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
OCTOBER, 1991
Keywords
BIOLOGY,, CONTROL,, CONIELLA,, LEAF,, SPOT,, KENAF,, HIBISCUS CANNABINUS,, INDUCED,, CONIELLA MUSAIAENSIS,, SUTTON VAR HIBISCI,, SUTTON.