Research Article
Open Access
Infection in Tuber Head, Middle and Tail by
Rhizopus stolonifer (Ehrenb.) Lind in Relation to Calcium
Content in Dioscorea rotundata Poir.
Otusanya MO*
Department of Crop protection, College of Plant Science and Crop production, Federal University of Agriculture Abeokuta, Nigeria.
*Corresponding author: Otusanya MO, Department of Crop protection, College of Plant Science and Crop production, Federal University of Agriculture Abeokuta, Nigeria; E-mail:
@
Received: July 13, 2018; Accepted: August 25, 2018; Published: November 28, 2018
Citation: Otusanya MO (2018) Infection in Tuber Head, Middle and Tail by Rhizopus stolonifer (Ehrenb.) Lind in Relation to Calcium Content in Dioscorea rotundata Poir.Int J Plant Stu. 1(1): 1-4.
AbstractTop
Calcium content in tuber head, middle, tail region in four white
guinea yam varieties (Dioscorea rotundata) was investigated in this
study in relation to infection by Rhizopus stolonifer. This is informed
by the observed higher sprouting/germination of “head” yam setts
than the middle or tail. The experimental design was 4 by 3 factorial
in randomized complete block arrangement of head, middle, tail per
block with three replications, and variety as main plot treatment.
After 4 weeks incubation, varietal mean infection of 1.32%, 1.45%
and 2.74%, for varieties Oniyere, Iseosi, Efuru respectively was
significantly lower than the 11.1% in variety Dakaa. There were no
significant differences in infection of head (4.24%), middle (2.9%) or
tail (5.33%) region, but middle region infection of 0.92% was lower
in variety Oniyere and Efuru. Mean tuber region calcium content
in mg/100g dry matter were not significantly different in variety
Oniyere (23.33), Iseosi (21.67) and Efuru (25), but all three were
higher than Dakaa (5.51). Head and middle region calcium of 6 and
6.08 mg/100g dm was lower than the 3.72 mg/100g dm of the tail in
variety Dakaa. Calcium role in the plant cell wall confers structural
integrity which resists pathogenic enzyme deterioration but
analysis of total phenolic compounds which may confer structural
integrity as well as toxic metabolites which destroy the pathogen
may render explanation to the “hardy” nature of yam tuber head
region compared to the middle and tail regions.
Introduction
Yams, Dioscorea species especially the white guinea yam
varieties, Dioscorea rotundata Poir are probably more popular in
South West Nigeria as food cultivars than the water yam, Dioscorea
alata L. The water yam in South West Nigeria is popular among
the Ijebu sect in Ogun state who prepare local dish refered to as
"Ikokore" from the grated cooked and spiced meal. Water yam
may also be peeled, grated, spiced, made into balls and fried into
a meal snack called “Ojojo”. Apart from these two, preparations,
the Yoruba in the South West relish various preparations from
White guinea yams which outnumber those for which water yam
is put. Also many whiter guinea yam varieties are available in a
yam (South West Nigeria) market relative to water yam varieties.
The South East Nigerian region however has numerous dishes/
preparations from water yam and relatively more water yam
varieties. Yoruba farmers in South West Nigeria plant sections
usually cut or prepared from whole tubers, which are refered to
as yam “setts”. The setts are preferred for the smallholder farmer
because ware yams are more costly for planting.
The alternative is the smaller-sized yams refered to as “seed yams” which are formed after the milk harvest (at six months after planting) when big-sized tubers are severed with sharp knives from the shoots in a yam mound. The severing is done such that a part of the proximal (head) region is left, still attached to the shoot. The latter are then buried again for the last 3 months (month 6 to 9) of the growth cycle when the severed portion bulks again to produce the small-sized yams at physiological maturity which are refered to as “seed yams”. The latter are usually expensive especially towards the onset of rains which is generally the time to plant yams. A small holder farmer buys as many seed yams as can be afforded financially and supplements with yam “setts” cut from the ware yams which normally may be as big as 2 to 6 kilogram weight. Ware yams are harvested at physiological maturity when yam leaves become senescent, generally 9 months for white guinea yam.
It is usual to have faster emergence from setts prepared from the proximal region/head region as farmers are familiar with rots affecting more setts from the distal portion of the tuber in the field. Differences in infection by Aspergillus niger from different geographical locations (Nigeria, Asia and Europe) on cut regions of the yam (Dioscorea species) tuber were not consistent probably because of a mix up of varieties from their sources (provenances) (Otusanya and Jeger, 1994).
Calcium fertilization in two improved varieties of Dioscorea spices namely D. rotundata TDr 131 and D. alata TDa 92-2 reduced infection by Aspergillus niger and Botryodiplodia theobromae after long-term storage, especially in yam sections/yam setts (Otusanya et al., 2016).
This study investigated infection in different regions namely head, middle and tail of tubers of four varieties of white guinea yam from South West Nigeria, by Rhizopus stolonifer, an important yam tuber rot pathogen. Calcium content of the head, middle and tail of tubers of the four varieties were also analysed to ascertain relationship between it and infection.
The alternative is the smaller-sized yams refered to as “seed yams” which are formed after the milk harvest (at six months after planting) when big-sized tubers are severed with sharp knives from the shoots in a yam mound. The severing is done such that a part of the proximal (head) region is left, still attached to the shoot. The latter are then buried again for the last 3 months (month 6 to 9) of the growth cycle when the severed portion bulks again to produce the small-sized yams at physiological maturity which are refered to as “seed yams”. The latter are usually expensive especially towards the onset of rains which is generally the time to plant yams. A small holder farmer buys as many seed yams as can be afforded financially and supplements with yam “setts” cut from the ware yams which normally may be as big as 2 to 6 kilogram weight. Ware yams are harvested at physiological maturity when yam leaves become senescent, generally 9 months for white guinea yam.
It is usual to have faster emergence from setts prepared from the proximal region/head region as farmers are familiar with rots affecting more setts from the distal portion of the tuber in the field. Differences in infection by Aspergillus niger from different geographical locations (Nigeria, Asia and Europe) on cut regions of the yam (Dioscorea species) tuber were not consistent probably because of a mix up of varieties from their sources (provenances) (Otusanya and Jeger, 1994).
Calcium fertilization in two improved varieties of Dioscorea spices namely D. rotundata TDr 131 and D. alata TDa 92-2 reduced infection by Aspergillus niger and Botryodiplodia theobromae after long-term storage, especially in yam sections/yam setts (Otusanya et al., 2016).
This study investigated infection in different regions namely head, middle and tail of tubers of four varieties of white guinea yam from South West Nigeria, by Rhizopus stolonifer, an important yam tuber rot pathogen. Calcium content of the head, middle and tail of tubers of the four varieties were also analysed to ascertain relationship between it and infection.
Materials and Methods
Yam, Dioscorea species tubers
Tubers of four varieties of white guinea yam Dioscorea
rotundata were sourced from the yam farmers’ market in
Gbonogun main market, Abeokuta, Ogun State in South West
Nigeria. They are varieties Efuru, Oniyere, Iseosi and Dakaa.
Analysis of Tuber Calcium
Three tubers per variety were selected for the tuber calcium
analysis. The selected tubers were free of abrasions or injuries
or disease symptoms. They were washed in running tap water
without bruising them and left to dry on top of a laboratory bench
under a low-speed fan. Each tuber was then cut into sections of
head, middle and tail. Each section was sliced thereafter into thin
chips inside labelled plastic trays. Drying of the chips was for three
days on yam storage structures inside the COLPLANT (College
of Plant Science and Crop Production), Federal University of
Agriculture, Abeokuta (FUNAAB), Screen house. The dried chips
were ground to powder with a high powered mill at the Central
Workshop of COLENG (College of Agricultural Engineering),
FUNAAB. They were then poured into new labelled polyethylene
bags for calcium content analysis. Analysis of calcium content
was carried out with the routine methods of mineral (Calcium)
analysis of the Association of Official Analytical Chemists [1].
Infection and weight loss experimental design and
procedure
Tubers which had no bruises, lacerations or disease rot
symptoms (soft, dry or wet) of the four varieties were selected.
They were cut into fairly equal regions of the head, middle, and
tail perpendicular to the tuber length, after the head and tail tips
had been cut off, with a sharp surface-sterilized steel knife [3].
They were left to dry for 24 hours on top of surface-sterilized
Laboratory benches in the Crop Protection Laboratory of the
Department of Crop Protection, COLPLANT, FUNAAB, Abeokuta,
Ogun State in the South West area of Nigeria. Each of these cut
regions of head, middle and tail from each tuber had two cut
surfaces and served as the experimental units [4]. Each yam
section was labeled and weighed with an electronic balance at
the beginning of the experiment. Cut sections of the four varieties
were then set up, in a 4 x 3 factorial experiment, arranged in
randomized complete block, each of head, middle and tail, and
three replications.
Each experimental unit was inoculated with a 7-day old pure culture of Rhizopus stolonifer which had earlier been isolated from a partially rotted tuber of variety Efuru. Inoculation of experimental units was according to the method of Otusanya and Jeger (1994). Surface sterilized 4 mm and 3 mm cork borers, scalpel and forceps were used to bore 10 to 12 mm hole into each unit and to place a 3 mm agar (potato dextrose agar) disc of the pathogen into the hole. After which the upper incision on the periderm was sealed with Vaseline (petroleum jelly). The inoculated sections were transferred in trays into a raised wooden netted/ventilated yam storage structure inside the COLPLANT screen house. The yam storage structures are protected from rain, rodents/reptiles and allow free air flow which disallows increase of humidity. Incubation period was 4 weeks. Each section was weighed again with an electronic balance after the 4 week incubation. Then, each yam section was cut open with a knife, after the Vaseline had been removed with spatula and cotton wool. Infected tissue was cut into a pre-weighed petri-dish and its weight measured with an electronic balance. Percent infection was determined with the formula:
Where C and A are corrected weight of infected tissue and weight of the yam section at the beginning of the experiment respectively. C was calculated with the formula: where X and Y are the weight of infected tissue and percentage weight loss respectively. Percent weight loss was calculated with the formula: , where A and B are weight of the section at the beginning and at the end of the experiment respectively.
Each experimental unit was inoculated with a 7-day old pure culture of Rhizopus stolonifer which had earlier been isolated from a partially rotted tuber of variety Efuru. Inoculation of experimental units was according to the method of Otusanya and Jeger (1994). Surface sterilized 4 mm and 3 mm cork borers, scalpel and forceps were used to bore 10 to 12 mm hole into each unit and to place a 3 mm agar (potato dextrose agar) disc of the pathogen into the hole. After which the upper incision on the periderm was sealed with Vaseline (petroleum jelly). The inoculated sections were transferred in trays into a raised wooden netted/ventilated yam storage structure inside the COLPLANT screen house. The yam storage structures are protected from rain, rodents/reptiles and allow free air flow which disallows increase of humidity. Incubation period was 4 weeks. Each section was weighed again with an electronic balance after the 4 week incubation. Then, each yam section was cut open with a knife, after the Vaseline had been removed with spatula and cotton wool. Infected tissue was cut into a pre-weighed petri-dish and its weight measured with an electronic balance. Percent infection was determined with the formula:
Where C and A are corrected weight of infected tissue and weight of the yam section at the beginning of the experiment respectively. C was calculated with the formula: where X and Y are the weight of infected tissue and percentage weight loss respectively. Percent weight loss was calculated with the formula: , where A and B are weight of the section at the beginning and at the end of the experiment respectively.
Data Analysis
Percent data was transformed appropriately before Analysis
of variance. Means were separated with Tukey’s (HSD) test.
Results
Infection in tuber head, middle and tail and calcium
content
Percent infection in the varieties was significantly different
(Table 1). Variety Dakaa had higher infection of 11.1% than the
three other varieties which were not significantly different from
one another, with the values 1.32% Oniyere/1.45% Iseosi/2.74%
Efuru. Tuber regions were comparable/similar in infection,
and the head region had 4.24%, the middle region 2.90% and
the tail region 5.31%. Interaction effects showed significantly
lower infection of 0.92% in the middle region of variety Oniyere,
whereas the head and tail which were comparable or similar
had 1.22% and 1.81% respectively. The middle of variety Efuru
with 0.92% was also significantly lower than the head and tail
which had comparable/similar infection of 4.02% and 3.27%
respectively. However, variety Iseosi had comparable infection in
all three regions of 1.3% (head), 1.41% middle and 1.63% (tail).
Higher overall mean infection than in the three other varieties
occurred in variety Dakaa which had 11.1% compared to the
other three varieties which had overall mean infection of over
1% each. The head middle and tail regions of variety Dakaa had
comparable/similar infection of 10.43% (head), 8.33% (middle)
and 14.53% (tail). Interaction effects indicated comparable
calcium content in the three regions in three of the four varieties
namely Oniyere, Iseosi and Efuru. Each of these varieties had
overall mean calcium content of over 21 mg/100 gdm in the three
regions. Variety Dakaa however had significantly lower overall
mean calcium content of 5.51 mg/100 gdm and also significantly
lower calcium in the tail of 3.72 mg/100 gdm compared to that of
the head (6 mg/100 gdm) and middle (6.8 mg/100 gdm) regions
which had comparable/similar calcium content.
Table 1:Infection by Rhizopus stolonifer in 4 weeks and calcium content in the head middle and tail region of the tuber of four varieties of white guinea yam, Dioscorea rotundata Poir.
Variety |
% infection |
Calcium mg/100gdm |
Content |
|
Oniyere |
1.32b |
23.33a |
||
Iseosi |
1.45b |
21.67a |
||
Dakaa |
11.10a |
5.51b |
||
Efuru |
2.74b |
25.00a |
||
TUBER REGION |
||||
Head |
4.24a |
18.38a |
||
Middle |
2.90a |
20.45a |
||
Tail |
5.31a |
17.81a |
||
INTERACTION |
||||
White variety |
guinea |
yam |
Tuber region |
|
Oniyere |
Head |
1.22b |
22.50a |
|
Middle |
0.92c |
22.50a |
||
Tail |
1.81b |
25.00a |
||
Iseosi |
Head |
1.30b |
17.50a |
|
Middle |
1.41b |
25.00a |
||
Tail |
1.63b |
22.50a |
||
Dakaa |
Head |
10.43a |
6.00b |
|
Middle |
8.33a |
6.80b |
||
Tail |
14.53a |
3.72c |
||
Efuru |
Head |
4.02b |
27.50a |
|
Middle |
0.92c |
27.50a |
||
Tail |
3.27b |
20.00a |
M eans in a column followed by the same letter are not significantly different at P = 0.05
Discussion
Overall mean infection of head, middle and tail regions of
the tuber in varieties Oniyere, Iseosi and Efuru in the 4 weeks
of incubation with Rhizopus stolonifer, was in the range 1.32%
to 2.74%. This mean was lower than in variety Dakaa which
had overall mean of 11.1%. However, there were no significant
differences in infection of the tuber regions. But interaction
effects in two of the four varieties namely Oniyere and Efuru
had significantly lower infection in the middle region than the
head or tail regions. The two other varieties, Iseosi and Dakaa
had comparable/similar infection in the head, middle and tail
regions. Head portions of yam (Dioscorea) tubers especially in
white guinea yam are known to be “hardy” than the middle or
tail regions and are naturally preferred as setts for planting as
they sprout easily and are less likely to rot after planting in the
field compared to the middle and tail portions. Farmers in Nigeria
are therefore more careful with setts prepared from the distal
portion of the tuber as emergence is usually known to be lower
with them except cultural management is high and supported
by management pesticides. Calcium fertilization (CaCO3) and
NPK reduced infection by Aspergillus niger and Botryodiplodia
theobromae especially in cut regions in two improved varieties of
Dioscorea species namely D. rotundata TDr 131 and D. alata TDa
92-2, after long-term storage [5]. This was the basis for calcium
content analysis in this study. But calcium content analysis in 3 of
the 4 varieties in this study had no significant differences in either
head, middle or tail. Only variety Dakaa had significantly different
calcium contents in the tuber regions. In this variety, calcium
content of 6mg/100gdm and 6.8 mg/100 gdm of the head and
middle region, were comparable/similar and higher than that of
the tail region which was 3.72 mg/100 gdm. Probably analysis of
total phenolic compounds of tuber regions of head, middle and
tail in white guinea yam (Dioscorea rotundata) may establish
which region is potentially higher in resistance to the tuber rot
pathogen Rhizopus stolonifer. Phenolics or phenolic compounds
have a wide variety of structure and potential which provides
basis for their specificity as antimicrobial agents [2].
ReferencesTop
- AOAC. Association of Official Analytical Chemists. Official Methods of Analysis. Washington DC. 1990.
- Dube HC. Modern Plant Pathology 2nd edition. Saraswati Purohit. Jodhpur. 2014;576.
- Otusanya, M. O. 1994. Studies on Yam (Dioscorea spp.) tuber rot caused by Aspergillus niger van Tiegh. M. Phil. Thesis University of Reading, United Kingdom. 119 pp.
- Otusanya MO, Jeger MJ. Infection of Yam Tubers by Aspergillus niger in relation to Isolate, Yam Species and Temperatures. International Biodeterioration and Biodegradation. 1994;33(4):319-331.
- Otusanya MO, Enikuomehin O, Popoola A, Adetunji M, Kehinde O and Okeleye K, et al. Effects of calcium fertilization on the susceptibility of Dioscorea species to the yam storage pathogens Aspergillus niger van Tiegh and Botryodiplodia theobromae pat. Journal of Plant Physiology and pathology. 2016;4(3).