Sisal/Agave - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 335

because natural fibers have largely been replaced by synthetic fibers [ 2 , 20 ,
23 ]. Recent increases can be attributed to increased production in Brazil and an
increase in interest in natural versus synthetic fibers for select markets (Fig. 15.1 ).
Most of the growing regions for Agave are semiarid, but Brazil also produces Agave
in areas with high rainfall (

1,000 mm) but that have few other present economic
opportunities relative to other regions of this resource-rich country.
The demand for natural fibers from sisal peaked in 1964, when

>

1 Mha of land
around the world was planted in Agave [ 20 ]. Since 2000, abandoned sisal produc-
tion, primarily in Africa and Mexico, has led to the abandonment of this agriculture
on 0.6 Mha of land globally (Fig. 15.1 )[ 20 ], and it is estimated that this land alone
could support an annual production of 6.1 billion liters of ethanol [ 2 ]. As of writing,
however, there is no commercial production of Agave for biofuel.
Agave crops can be grown in a wide variety of conditions, but the greatest
opportunity (economically and geographically) probably exists on semiarid lands
that currently do not support other valued crops. Semiarid lands are classified by the
United Nations Environment Program as areas where the ratio of actual to potential
evapotranspiration is between 0.2 and 0.5 and total precipitation is typically less
than 600 mm. Such land represents 17.7 % of the land surface or 2,370 Mha [ 24 ].

>

Genetic Resources

Regardless of the opportunities, there is still a need for research on the yield
potentials of different Agave varieties for different regions. Yields reported in
previous literature reflect a variety of growing conditions and managements
(Table 15.2 ). Large-scale replicated yield trials, and in particular trials comparing
varieties, have not been conducted to date, but these will be critical to understand
the true potential of Agave as a bioenergy crop [ 2 ]. There is a wealth of genetic
diversity in the genus Agave that has been qualitatively described, but a central
depository of defined germplasm for the genus is lacking [ 7 , 25 ]. Cultivars can be
triploid or pentaploid sterile interspecific hybrids, often precluding conventional
genetic analysis and further breeding in these lines. However, the rapid growth of
sequencing capability and analysis is contributing to a better understanding of inter-
and intraspecific variation and genetic resources related to diseases, pest resistance,
and environmental resilience [ 26 - 29 ]. This should also provide molecular markers
to accelerate breeding. However, targeted breeding efforts have not yet been
undertaken to optimize Agave as a biofuel feedstock.