Fusarium wilt race 3 was discovered on several commercial farms on the west coast of Florida in the spring of 1982. In order to find resistance to this pathogen, approximately 900 genotypes ranging from wild species to established cultivars were screened by the standard root dip technique. Seed was saved from all healthy plants and rescreened along with numerous hybrids from crosses of resistant and susceptible inbreds. A number of L. peruvianum and L. glandulosum accessions had good resistance (Table 1) . Several other genotypes had high levels of resistance and underwent considerable testing. Of these, the best level of resistance was found in LA 716, an L. pennellii accession. Ten individual plant crosses were made between LA 716 and 'Hayslip' and these were screened 2 times (Table 2). Gene action for most hybrids is difficult to explain, but the hybrid derived from LA 716-8 appeared to have resistance conferred by dominant gene action.
Two breeding lines with 100% resistance were developed from this hybrid. One, 657-1, was derived by a backcross of the F1 to a susceptible inbred followed by 2 generations of selfing after disease screening. The second, 672-1, was an F4 derived from the F1. Both lines were crossed with susceptible cultivars. and Fl, BCP1, BCP2, and F2 seed were obtained. These 2 families were screened in the summer of 1985. Results, although preliminary due to shortage of seed, tend to favor a single dominant gene conferring resistance to fusarium wilt race 3 (Table 3).
Obviously, this conclusion needs to be confirmed by screening greater numbers of plants which recently have been obtained. Most, but not all, F2 data from a backcrossing program support the single dominant gene hypothesis. The data reported here document both our progress to date, and also some of the anomalies which have occurred in this work. Possibly, data such as that in Table 2 are more the rule than the exception in this type of work, but such data might go unreported because it is not easily interpreted. Explanations of the data will not be made here. If further experimentation supports control of resistance by a single dominant gene in 657-1 and 672-1, these genetic lines will be made available to those who request them. In addition to determining the genetics of this resistance, we are in the process of studying the relationship of this resistance with I and I-2. LA 716 is resistant to these 2 races as well.
Table 1. L. peruvianum and L. glandulosum accessions with lowest Fusarium wilt race 3 incidence from 1982 and 1983 seedling inoculation experiments at Bradenton, Florida.
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Experiment 1 Experiment 2
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No. No. No. No.
PI Number^z^ Healthy Diseased Healthy Diseased
126431 19 0 39 1
126441 18 1 88 6
126928 20 0 31 1
126930 17 1 37 0
126935 20 0 29 3
127831 18 1 98 15
127832 18 1 95 2
128643 11 0 30 3
128645 19 0 27 0
128646 20 0 -- --
128647 20 0 31 1
128648 20 0 29 8
128649 20 0 31 1
128650 19 0 15 1
128653 20 0 29 2
128655 20 0 - --
128656 19 0 -- -
128657 36 4 105 20
128659 20 0 27 4
128661 35 5 -- --
128663 32 6 51 2
246585 18 1 16 2
247807 17 0 -- --
251306 19 0 14 5
266375 20 0 20 0
126440* 20 0 30 1
126444* 20 0 32 0
199380* 18 2 59 7
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All L. peruvianum except * indicate L. glandulosum.
Table 2.
Fusarium wilt race 3 incidence after seedling inoculation of
Hayslip, LA 716, and 10 hybrids between Hayslip and individual
plants of LA 716 at Bradenton, Florida, 1983.
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First Screen, August 1983 Second Screen, October 1983
_________________________ ___________________________
No. No. No. No.
Genotype Healthy Diseased Healthy Diseased
Hayslip 1 9 0 10
LA 716 16 0 9 0
(HayslipxLA716-1) 13 7 - --
(HayslipxLA716-2) 7 13 16 4
(HayslipxLA716-3) 13 7 15 5
(HayslipxLA716-4) 15 5 17 3
(HayslipxLA716-5) 14 6 - --
(HayslipxLA716-6) 14 6 9 3
(HayslipxLA716-7) 4 16 5 5
(HayslipxLA716-8) 17 1 19 1
(HayslipxLA716-9) 3 17 14 4
(HayslipxLA716-10) 8 4 3 16
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Table 3.
Fusarium wilt race 3 reactions for families of two resistant
inbreds derived from LA 716 at Bradenton, Florida, Summer 1985.
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Number of Plants
________________ Expected Chi
Genotype Generation Healthy Diseased Ratio Square P
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672-1(F4) P1 34 0 1:0
Horizon P2A 0 39 0:1
Hayslip P2B 2 34 0:1
(Horizonx672-1) F1 24 0 1:0
672-1
(Hayslipx672-1) BCP1 19 3 1:0
Hayslip
(Hayslipx672-1) BCP2 7 8 1:1 0.066 .5-.9
(Hayslipx672-1)-BK F2 25 7 3:1 0.267 .5-.9
657-1 (F1BC1S2) P1 2^z^ 0 1:0
Suncoast P2 4 27 0:1
(Suncoastx657-1) F1 29 5 1:0
657-1
(Hayslipx657-1) BCP1 11 0 1:0
Suncoast
(Suncoastx657-1) BCP2 8 9 1:1 0.058 .5-.9
(Suncoastx657-1)-BK F2 30 3 3:1 4.455 .01-.05*
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^z^Other tests had 25 healthy plants and 0 diseased.