Production Practices and Quality Assessment of Food Crops. Vol. 1

150 S. Pereira-Lorenzo and A. M. Ramos-Cabrer
In Europe, genetic variability between natural chestnut populations was
studied by Pigliucci et al. (1990a and b), Villani et al. (1991a and b, 1993) and
Aravanopoulos (2002). These works established a gene flow from Orient (Turkey)
to the Occident (Italy). In United States similar studied were performed on wild
populations of the American chestnut (Huang et al., 1994b, 1996b and 1998) using
both isoenzymes and RAPDs.
In Portugal, analysis of the genetic variability in cultivars was studied by isoenzymes
(Pereira et al., 1999), with RAPDs by Valdiviesso (1999) and RAPD and
ISSR by Goulao et al. (2001). In Spain, the genetic variability between C. sativa,
C. crenata, C. mollissima and interspecific hybrid clones was studied by isoenzymes
by Fernandez-Lopez (1996). Pereira (1994) and Pereira-Lorenzo et al. (1996b,
1997b) studied the variability of the Galician chestnut cultivars by isoenzymes
confirming the high variability found by morphology. However, Fineschi et al. (1994)
showed a relatively high degree of homogeneity both among individuals of the same
variety and among varieties of the same area but a high genetic distance between
geographic areas in Italy.
Studies about the American species C. pumila var. ozarkensis showed that the
level of diversity is lower than in Chinese and European chestnut populations, this
perhaps reflect the mortality caused by blight (Dane et al., 1999). Huang (1998)
showed a negative correlation between genetic distance and geographic distance
between chestnut populations in America and suggest a limited gene flow and
possible geographical isolation. Populations from Alabama showed a high level of
genetic diversity and this could be related with glacial refugia.
Linkage relationships of isoenzymes and morphological traits in interspecific
crosses were found (Huang et al.,1996a). Recently, molecular maps have been developed
(Kubisiak et al., 1997 and Casasoli et al., 2001), opening a new way to the
knowledge about the genetics of chestnut.
9.2. Propagation
Incompatibility between some interspecific hybrids and cultivars from C. sativa
(Breisch, 1995; Pereira-Lorenzo and Fernandez-Lopez, 1997a; Craddock and Bassi,
1999) are restricting the use of these as rootstocks resistant to ink disease.
In micropropagation, though important advances have been made, the selection
of culture medium, carbon source, rooting stage and acclimatisation needed further
studies (Ballester et al., 2002). Somatic embryogenesis as an alternative to clonal
system is being explored for chestnut, as well as a tool in genetic engineering
programmes (Carraway and Merkle, 1997; Xing et al., 1999, Ballester et al.,
2002).
Improvement in propagation by cuttings has reduced the practice of layering.
However, propagation by cuttings needs expensive facilities such as heated greenhouses
with fog system, and clonal variation in rooting reduces the importance in
transferring this technique from research to nursery production.