Sisal/Agave - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 334

stage is initiated, these carbohydrate reserves are mobilized to elongate the stem
into an enormous flowering spike. For tequila production, the stem base must be
harvested just before spike development. Cultivars of Agave tequilana have been
selected for early flowering time relative to other Agave spp. so it can be harvested
in 5-year rotations. Other species will mature after a decade or longer.
Agave spp. that are grown for fiber have long straight leaves from which long
fibers can be harvested for rope and fabrics. Agave sisalana (sisal) is the most
widely cultivated, primarily in Africa and South America, where this crop occupied
roughly 420,000 ha in 2010 declining from 890,000 ha in 1961 [ 20 ]. Another fiber
variety, A. fourcroydes (henequen), is mainly grown in Mexico and occupied
43,000 ha in 2010 [ 20 ]. These plants also produce soluble carbohydrates
(Table 15.1 ), but would be most suitable as lignocellulosic feedstock crops. The
leaves are harvested instead of the whole plant, as in an A. tequilana crop, and
biomass from the same plants can therefore be harvested repeatedly at a shorter
interval than is typical for the tequila crop. The opportunity to repeatedly harvest
leaves from sisal and henequen plants offers a potentially continuous supply of
feedstock for lignocellulosic fuel production. Currently, most harvesting is manual,
which may be an important source of income in the poorest countries. Elsewhere,
viability is likely to depend on mechanical harvesting. However, both manual
harvesting aids and sisal harvesters have been proposed and tested [ 21 , 22 ].
Brazil is currently the largest producer of Agave for sisal fiber (Fig. 15.1 ). Other
leading producers, including Tanzania, Kenya, Madagascar, and Mexico, suffered a
decline in production since the late 1960s, but most dramatically since 2000,
Fig. 15.1 World production of Agave fibers, 92 % of which are sisal, showing the contribution of
Africa (primarily Tanzania, Kenya and Madagascar), Brazil, and all other countries (Based on data
from Ref. [20])