Thesis (Ph.D. Agriculture (Plant Production)) -- University of Limpopo, 2020 / Worldwide, both root-knot (Meloidogyne species) and sugarcane aphid (Melanaphis
sacchari Zehntner), are economic pests on sugarcane and sorghum crops. In most
cases, each of the two pests is managed using host plant resistance due to the
economic benefits derived from this management strategy. The highly nematode
resistant sweet stem sorghum (Sorghum bicolor L.) cv. 'Ndendane-X1' used in ethanol
production, is highly sensitive to sugarcane aphid, with some indication that the latter
could interfere with nematode resistance in the sorghum cultivar. This study had four
objectives which collectively intended to investigate the interactive effects of infection
by three Meloidogyne species and infestation by aphid under different conditions on
resistance to nematode in a nematode-resistant sorghum cultivar. The research
objectives were achieved through four trials. In each trial a 2 × 2 factorial experiment,
each with and without nematode and aphid as first and second factors, respectively,
were conducted. Treatments were arranged in a randomised complete block design,
with six replications, and each experiment validated in time. At 150 days, after
emergence, the nematode × aphid interaction significantly reduced sucrose by 17, 74
and 42% in Meloidogyne enterolobii, Meloidogyne incognita and Meloidogyne javanica
trials, respectively. Aphid infestation of sorghum significantly increased the
reproductive potentials of the three respective Meloidogyne species by 196, 320 and
152%, but significantly, reduced plant growth variables from 20-44 and 48-51% in two
respective trials. The mineral nutrients S and Zn were reduced in leaf tissues of the
test cultivar in Trial 1, whereas Ca and Zn were respectively reduced by 24 and 51%
in Trial 2 and by 52 and 51% in Trial 3. Since the reproductive potential values for
Meloidogynqe species on the test sorghum cultivar were greater than unity and
nematode infection reduced the plant variables, cv. 'Ndendane-X1' lost resistance to xx
the test Meloidogyne species. In achieving Objective 2, procedures were similar to
those in Objective 1 except that the study was conducted under field conditions under
mixed nematode populations of M. enterolobii, M. incognita and M. javanica. Sorghum
seedlings were raised at 0.3 m × 0.3 m inter and intra row spacings. Soon after
emergence, plants were thinned to one per station, randomly selected for nematode
and nematode-aphid treatments. Mixed populations of Meloidogyne species (M.
enterolobii, M. incognita and M. javanica) at approximately 1:1:1 (v/v) ratio were
applied at 300 eggs + J2 per plants after thinning at the five plants which were used
as nematode alone treatments. The latter were also infested with 20 sugarcane aphids
to constitute a nematode + aphid treatments. Buffer zone plants separating the
treatments were monitored for aphids and stock borer, which were sprayed when
necessary. At 150 days after infestation, relative to nematode alone, nematode-aphid
significantly reduced degrees Brix from 13% to 61%, but significantly increased the
reproductive potential of mixed Meloidogyne species and root galls by 279 and 199%,
respectively. Also, the combined effect significantly reduced plant growth variables
from 35 to 55% and the mineral nutrient elements in leaf tissues of the cultivar from
33 to 73%. At 150 days after the treatment, the second and first order interaction
(Nemarioc-AL × Nemafric-BL × Mordica and Nemafric-BL × Mordica) had significantly
increased sucrose content from 48 to 66%, increased plant growth variables from 49
to 163%, increased accumulation of certain nutrient elements from 164 to 206%. The
terpenoid-containing phytonematicides could have potential future application in the
husbandry of ethanol-producing sweet stem sorghum cultivars in relation to increasing
sucrose above the 16% minimum for premium delivery fees and increased plant
growth. Under field conditions, in pest-free condition (Objective 3), drenched
terpenoid-containing phytonematicides significantly increased sucrose content at xxi
middle and bottom part of SSS cv. 'Ndendane-X1' by 66 and 48%. However, these
products did not significantly increase plant variables, except tiller number, which was
increased by 163 under first order interaction from Nemafric-BL and Mordica
phytonematicides. Similarly, nutrient elements variables had generally not been
increased by the interaction of these products, except Ca and K, which were increased
by 206 and 164%. In achieving Objective 4, a 2 × 2 × 2, with the first, second and third
factor being Nemarioc-AL (with and without), Nemafric-BL (with and without) and
Mordica (with and without) phytonematicides, respectively. on sorghum cultivar
infected with a mixture of Meloidogyne species and infested with aphids, under
microplot conditions, untreated control sucrose content remained below the standard
of 16 degrees Brix, whereas the second order interaction increased the variable far
above the standard, along with various plant growth variables also increased.
However, both nematode and aphid population densities were significantly reduced by
the interactions. Findings in this thesis constituted the first report where aphid
infestation broke resistance to Meloidogyne species in sweet stem sorghum cv.
'Ndendane-X1'. Therefore, the successful use of nematode resistance in the cultivar
in areas with high nematode population densities would depend upon the effective
management of the sugarcane aphid population densities. Also, the three terpenoid-containing phytonematicides would when combined or used alone have the potential future in the husbandry of sweet stem sorghum cultivars intended for ethanol
production and suppression of nematode population densities / National Research Foundation (NRF)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3372 |
| Date | January 2020 |
| Creators | Maleka, Koena Gideon |
| Contributors | Mashela, P. W., Pofu, K. M. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xxii, 122 leaves |
| Relation |
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