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P-90<br />
Genetic control of phyllotaxy phase shift in juvenile vines in a rootstock hybrid population<br />
Peter Cousins<br />
USDA-ARS, Grape Genetics Research Unit, Geneva, New York, USA<br />
Corresponding author: Peter.Cousins@ars.usda.gov<br />
Grapevine seedlings initially display spiral phyllotaxy of true leaves, then undergo a shift to<br />
alternate phyllotaxy <strong>with</strong> the production of the first lateral meristems (typically tendrils). The<br />
node at which the shift from spiral to alternate phyllotaxy occurs varies from about the 4th to<br />
about the 12th node on the vine. To investigate the genetic control of the transition from spiral<br />
phyllotaxy to alternate phyllotaxy, a population segregating for this trait was developed <strong>and</strong><br />
screened. The population derived from four female parents <strong>and</strong> six male parents crossed in a<br />
Design 2 mating array (all female parents crossed to all male parents). The female parents were<br />
the pistillate flowered rootstock varieties 1613 Couderc, 93-5 Couderc (California clone), Vitis<br />
rupestris 187G, <strong>and</strong> Fercal. The male parents were staminate flowered grape rootstock<br />
germplasm, species, <strong>and</strong> species hybrid selections <strong>with</strong> diverse backgrounds, including<br />
accessions from the USDA ARS National Clonal Germplasm Repository, Davis, California<br />
(denoted <strong>with</strong> DVIT accession numbers): IAC 572, Vitis labrusca Y137 DVIT 1392, Vitis hybrid<br />
Y93 DVIT 1519, Vitis hybrid Q126 DVIT 1456, Vitis hybrid Q130 DVIT 1466, <strong>and</strong> Vitis hybrid<br />
R127 DVIT 1490. The species background of the male parents includes V. labrusca, V.<br />
mustangensis, V. riparia, V. tiliifolia, <strong>and</strong> V. rupestris. Seedlings from controlled crosses were<br />
grown in individual pots in a greenhouse <strong>with</strong> artificial illumination to provide 24 hours day<br />
length throughout cultivation. The node number of the first observed lateral meristem was<br />
recorded; the goal was 50 seedlings per population for each of 24 populations, although some<br />
populations showed poor seed germination. The transition from spiral to alternate phyllotaxy<br />
does not appear to be under simple genetic control, but there is significant variation from family<br />
to family in this trait. It should be possible through selection to increase the node number of the<br />
transition from spiral phyllotaxy, which is lateral meristem free, to alternate phyllotaxy.<br />
Reduced tendril counts on rootstocks would increase the efficiency of grape rootstock cutting<br />
production in nurseries.<br />
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