- THE FLORICULTURE VEGETATIVE CUTTING INDUSTRY 155
in the finish environment. The goals are for the cutting to be easily
extracted from the propagation tray by developing a root system that
fills the liner cell and to possess sufficiently compact and firm shoots to
withstand physical stresses associated with shipping and transplant.
The general recommendation is to provide a PPF between 500 and
800 μmol⋅m−^2 ⋅s−^1 which results in a DLI of 10–15 mol⋅m−^2 ⋅d−^1 (Blan-
chard et al. 2006; Currey et al. 2012). These light levels will further pro-
mote root and branch development, reduce internode elongation, and
increase stem diameter (Currey et al. 2012). The recommended air tem-
perature range is from 20◦Cto24◦C during the day and 16◦Cto20◦C
during the night. During Stage 4, the substrate is allowed to further dry
down between irrigation events (Dole and Hamrick 2006).
V. CASE STUDIES
A. Zonal Geranium
Geranium production starts with culture-indexing of selected, true-to-
type plants for vascular wilts and viruses. The major vascular wilts are
caused by a bacterium,Xanthomonas campestrispv.pelargonii,and
a fungus,Verticillium albo-atrum. Symptoms for these wilts do not
often appear until the cuttings have grown into mature plants and are
exposed to warm temperatures and high light. Chemical controls are not
effective; thus, preventing infection during the stock-plant process is
essential.
Culture-indexing is a system of redundant testing for vascular
pathogens coupled with intensive selection and sanitation procedures.
This process for creating clean stock includes testing individual cut-
tings for bacterial and fungal contamination over multiple generations,
followed by virus-indexing, which consists of heat treatment, meris-
tem tip culture, and virus testing with ELISA technology. Tissues may
also be tested for the presence of viruses with bioassays where tissue
is extracted from a cutting, macerated, and swabbed onto a susceptible
host plant. Culture-indexing for pathogens focuses on redundant test-
ing procedures, one-way flow of plants and human traffic, stringent san-
itation procedures, and annual renewal of the stock plants. The entire
process of creating clean plants to become elite stock may require up to
an year to complete.
Once the initial cuttings are determined to be clean in the lab,
they are sent to a stock-plant producer to be placed in the elite stock
house, or nucleus block. Cuttings harvested from the nucleus block are