Agriculture Reference
In-Depth Information
threshold soil temperatures and incremental
reductions in nematode resistance with each
degree above 78 °F, such that at 91 °F tomato
plants are fully susceptible. This would suggest
that in Florida, use of these varieties may have to
be restricted to spring plantings when cooler soil
temperatures prevail.
In bell pepper, two newly developed root-knot
nematode-resistant varieties (Charleston Belle
and Carolina Wonder) confer a high degree of
resistance to the root-knot nematode; however,
expression of resistance is heat sensitive. Further
research is necessary to characterize the useful-
ness of these varieties under the high soil tem-
perature conditions of Florida. Like tomato, use
of these varieties may have to be restricted to
spring plantings when cooler soil temperatures
prevail.
Susceptibility of bell pepper (Charleston
Belle, Carolina Wonder, Keystone Resistant
Giant, and Yolo Wonder B) to M. incognita
increased as temperature increased from 24 to
32 °C. Reproduction factor of M. incognita and
root galling increased (P < 0.05) for all cultivars
as temperature increased (Table 9.3 ). Overall,
reproduction of M. incognita and severity of root
galling on the resistant isolines Charleston Belle
and Carolina Wonder were less (P < 0.05) than
on susceptible Keystone Resistant Giant and
Yolo Wonder B, and the two cultivars within
each group did not differ. However, temperature
x cultivar interaction was found (P < 0.05) for
reproduction index and root galling (Thies and
Fery 1998 ).
In grapevine, the number of galls and egg sacs
of M. javanica increased with time and tempera-
ture on both rootstocks, although not signifi cantly
in all cases (Table 9.4 ). This increasing infesta-
tion with time can be ascribed to normal popula-
tion increase with increasing degree days
(Loubser 1988 ). Furthermore, pathogenicity as
measured by the degree of galling also appeared
to increase with increasing temperature. This was
more evident on the moderately resistant root-
stock 143 B Mgt ( Vitis vinifera x V. riparia )
[compared to the susceptible rootstock Jacquez
( Vitis aestivalis x V. cinerea x V. vinifera )] where
the number of eggs increased signifi cantly (and
galling apparently also) between treatments B
and C, irrespective of the number of degree days
which remained the same. The reason for this
was seen as a breakdown in resistance at the
Fig. 9.2 Diagrammatic representation showing the com-
plete loss of root-knot nematode resistance conferred by
the Mi gene in tomato with increasing soil temperature
Table 9.3 Comparison of four bell pepper cultivars differing in resistance to southern root-knot nematode grown at 24,
28, or 32 °C on reproductive index and root galling 8 weeks after inoculation with Meloidogyne incognita
Reproductive index x
Gall index y
Temperature/cultivar
24 °C
28 °C
32 °C
24 °C
28 °C
32 °C
Charleston Belle
0.3 a z
4.9 b
24.7 c
1.53 a
2.46 b
3.61 c
Keystone Resist. Giant
6.1 c
32.2 de
29.9 f
4.79 d
7.62 e
8.74 f
Carolina Wonder
0.1 a
4.0 b
22.9 c
1.57 ab
2.37 ab
3.55 c
Yolo Wonder B
4.7 c
29.4 de
125.8 ef
4.37 cd
7.82 ef
8.61 ef
x Reproduction index (fi nal population/initial population) of M. incognita
y Gall index: 1 = no galls, 2 = 1-3 %, 3 = 4-16 %, 4 = 17-25 %, 5 = 26-35 %, 6 = 36 %-50 %; 7 = 51-65 %, 8 = 66-80 %,
and 9 = greater than 80 % of root system galled
z Mean separation within columns by Duncan's multiple range test at P
0.05. Means were compared across all
temperature and cultivar combinations
 
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