Biology Reference
In-Depth Information
and/or set viable seed under the shorter frost-free growing season (Bell et al. 1972;
Eberlein and Fore 1984). Kochia is a prolific seed producer - up to 30,000 seeds
per plant (Stallings et al. 1995). Mature seed is readily germinable, and kochia ger-
minates early in spring when soil temperatures are relatively cool (Nussbaum et al.
1985). It has a sustained emergence period and may emerge after in-crop herbicide
application (Mickelson et al. 2004). Although only limited controlled-environment
germination research has been conducted on this species (Everitt et al. 1983; Jami
Al-Ahmadi and Kafi 2006), data indicate that kochia can germinate over a wide
range of temperatures. It is possible that selection of ecotypes differing in germina-
tion response or days to flowering may have contributed to its northern spread;
however, no information is known of possible Canadian latitudinal/climatic
ecotypes.
Climate change is expected to impact weed communities, including kochia.
Kochia and Russian thistle utilize the rarer C4 photosynthetic pathway and therefore
are ideal indicator species to track climate change effects and impact of the frequent
hot, dry conditions of the Prairies in recent years. In the past 40 years, the growing
season in the Prairies has increased by 1-4 days; the 1990s were the warmest on
record (Gitay et al. 2002). Bioclimatic modelling is useful in assessing the impact
of changes in climate on pest population distribution (Olfert and Weiss 2006;
Rogers et al. 2007), and is being used to predict the suitability of specific agroeco-
systems for survival and reproduction of kochia under selected climate-change
scenarios (Olfert, unpublished data). Climate change on the Prairies may facilitate
invasions of new weedy alien species introduced as a result of contamination of
seedlots of more adaptable crop species or varieties.
Kochia was the first weed species reported to evolve herbicide-resistant biotypes
in western Canada (Morrison and Devine 1994). Only one Russian thistle resistant
biotype was documented in the Prairies in 1989, with no reported cases until 2007
(Beckie, unpublished data). Herbicide-resistant kochia biotypes have spread dra-
matically since 1988, with reports of over 80% of populations in some areas show-
ing some level of ALS inhibitor resistance (Beckie et al. 2008, unpublished data).
Because ALS inhibitor resistance is frequently endowed by a single dominant or
semi-dominant nuclear gene, resistance alleles can move via seed or pollen
(Mallory-Smith et al. 1993; Stallings et al. 1995). Prolific seed production and rapid
turnover of the soil seedbank (Burnside et al. 1981) increase herbicide resistance
evolution in kochia. In the USA, ALS inhibitor-resistant kochia has no detectable
fitness penalty (Peterson 1999). However, a pleiotropic effect (i.e., one gene affects
several traits) of the ALS mutation on germination response was reported.
Germination of ALS inhibitor-resistant kochia occurred at cooler soil temperatures
and/or more rapidly than susceptible kochia and was presumed to be due to the ele-
vated levels of branched-chain amino acids that result from the mutation (Dyer et al
1993; Thompson et al. 1994). Greater and more rapid germination and emergence
of resistant kochia than that of susceptible kochia in cool soil in spring may impact
both competitiveness and invasiveness (northerly range expansion).
Genetic diversity is the heritable variation within and among populations of a
species, and provides the opportunity for a population to evolve under changing
