Clonal variability among grower bulb lots of Easter lily 'Nellie White'

Potted Easter lily (Lilium longiflorum Thunb.) ranks among the top five potted flowering plants in the United States in economic value. One clone ('Nellie White') dominates the North American market. It is grown by less than 10 bulb producers, each maintaining their own propagation stock and practicing intraclonal strain selection. Greenhouse forcers attest to forcing differences depending on the bulb grower. The objective of this study was to determine the extent and sources of morphological variability among bulb growers. Bulb lots were obtained in 2002 (S1) and 2003 (S2) (n = 11 and n = 12 lots respectively) with 12 or 15 bulbs/lot. Grower's identification was confidential but kept consistent across shipment years. Bulbs were obtained as the 20.3 to 22.9-cm circumference commercial class, and S1 and S2 shipments were control temperature forced over two forcing cycles (FC1, FC2). Data collection included initial bulb weight and circumference; days to stem emergence (SEM), visible flower bud (VFB), and anthesis (AN); plant and inflorescence height; number of stems, leaves, flowers, and ovules per first flower/stem reaching AN; percentage of ovules forming viable seeds; leaf length and width; major lily viruses (presence/absence, relative optical density); leaf length-to-width ratios; AN-SEM, AN-VFB, and VFB-SEM. Significant differences were found among bulb lots for every trait except AN-VFB. Variability among bulb lots can be attributed to variation in initial bulb size, previous forcing cycle environment, variable lily symptomless virus (LSV) titer, and underlying genetic/epigenetic differences. Bulb circumference had the highest standardized canonical coefficient for canonical variable one in S2-FC1 and was a significant covariate in analysis of covariance; larger bulbs tended to produce larger plants. Forcing over two cycles allowed for less phenotypic variability among bulb lots in FC2 because of a common FC1 environment. All lilies were positive for LSV and negative for four other viruses tested. Significant negative correlations in S2 between relative optical density and plant height (FC1), initial bulb weight (FC2), and initial bulb circumference (FC2) indicate an effect of relative LSV titer on plant morphology. The role of LSV titer and genetic/epigenetic intergrower variability in 'Nellie White' warrants further investigation. Likewise, a lack of breeder/producer companies and the corollary independent grower strain selection has significant genetic consequences and complicates identification of superior 'Nellie White' clones.