Plot and planting
materials
This study was carried out at farmer’s farm in
Semenyih Selangor in July to November 2020. Virus-free sweet potato (variety
Lembayung) cuttings that collected from MARDI Bachok Kelantan were planted in
polybags contained of coco peat media at hot spot area of farmer’s farm in
Semenyih Selangor. Chives that propagated in a glasshouse at MARDI Serdang were
used as a companion crop in this study. Chives that planted at ratio 1:2
(chives: sweet potato) two weeks prior to sweet potato planting were used as a
treatment in this study meanwhile, sweet potato planted without chives were
used as a control. This experiment was arranged in completely randomized
design.
Leaf gas exchange
parameters
Leaf gas exchange parameters of sweet potato were
measured using a Portable Photosynthesis System (LI-COR 6400, LICOR Inc.,
U.S.A.) at 70 days after planting. Photosynthetically active radiation (PAR) of
the leaf chamber was set at 1200 ?mol m-2 s-1. The
chamber temperature was maintained at 30? and the reference CO2
concentration was 400 ppm (?mol mol-1). Relative humidity was
controlled between 50-70% with airflow rate at 500 ?mol s-1. The gas
exchange measurements were done on the mature, unshaded and completely expanded
leaves; between 0800 to 1100 h, which photosynthetic rates would be maximal
[7]. The leaf gas exchange for net photosynthesis rates (A) (?mol m-2
s-1) of virus infected and healthy plants were recorded and
statistically analysed.
Monitoring of pest
vector and beneficial insect in sweet potato cultivation
Monitoring of pest vectors (aphid and whitefly) and
beneficial insect were conducted using scouting, yellow sticky trap (YST) and
sweeping methods for three times throughout the planting season. In each
monitoring; pest vector was monitored using ten random scouting/ treatment,
five YST/treatment and five sweeps / treatment. Scouting was done by direct
counting of the presence of aphid and whitefly on ventral side of five apical
leaves in ten random plants. YST was placed at appropriate boundaries in the
plot and collected after 24h. The arthropod caught on each YST and sweeping
were identified and classified by their Order and Family. Mean number of aphid
and whitefly population in sweet potato planted with chives and control were
evaluated and statistically analysed.
Monitoring of incidence
and identification of virus in sweet potato cultivation
Virus incidence was scored for three times throughout
the planting season. The presence of virus symptoms on sweet potato leaves
grown with chives and without chives were recorded quantitatively. Disease
incidence percentage is calculated following the equation:
Disease incidence percentage = (Symptomatic plant/
whole plant population) X 100
Virus identification process that involve of RNA
extraction and cDNA synthesis was carried out using HiScript II One step RT-PCR
kit (Vazyme) following the manufacturer’s manual. Polymerase chain reaction
(PCR) was performed using specific primers for different viruses. The PCR
products were then cloned and sent for sequencing analysis. A derived DNA
sequence of the main virus was registered in National Center for Biotechnology
Information (NCBI).
Statistical analysis
The data generated from monitoring of pest vector,
beneficial insect and virus incidence were subjected to statistical analysis
using one-way ANOVA without interaction (SAS 9.4). The means significance
differences for pest vector and disease incidence of sweet potato planted with
chives and control were then performed using Duncan’s multiple range tests (the
minimum significance was set at P < 0.05).
Chemical compound
analysis of chives
Chemical compound analysis of chives was carried out
using five grams of powdered sample of chives that mixed with 45 mL methanol at
a ratio of (1:9). The samples were continuously shaken for 7 hours at 250 rpm
and subsequently filtered with a filter paper no 1 (Whatman) into a conical
flask. Two mL methanol extract of chives was then transferred into a GC vial
and injected into a GC-MS. The GC-MS instrumentations consisted of a gas
chromatograph mass spectrometer (GC/MS) analysis performed on an Agilent 7890A
gas chromatograph (GC) directly coupled to the mass spectrometer system (MS) of
an Agilent 5975C inert MSD with triple-axis detector. The column used was
DB-5MS UI (Agilent Technologies) with 30m length, 0.25 mm diameter with a
stationary phase of 5% phenyl methylpolysiloxane, 0.25 ?m film thickness. An
identification of peaks were done by a MSD Chemstation to find all of the peaks
in a raw GC chromatogram. A library search was carried out for all the peaks
using the NIST/EPA/NIH version 2.0. Selective compounds for sulphide components
as active compounds were determined.
Partial budget analysis
This study had employed partial budget analysis
towards chives planting for controlling virus transmission in sweet potato
cultivation. Partial budgeting is a consistent method for calculating the
expected change in profit from a proposed change in the farm business without
determining the absolute profit. The essentials parameter that taken into
account includes additional cost incurred, lost or reduction of current income,
additional income received and reduction or elimination to the current cost. The
analysis done using this partial budgeting was adapted from [8].
