cotton - Greenmount Press

The contribution of new varieties
to cotton yield improvement
■ By Shiming Liu, Peter Reid, Warwick Stiller and Greg Constable, CSIRO Plant Industry, Narrabri
AT A GLANCE…
Analysis of a large data set of CSIRO cotton breeding
experiments over 30 years has demonstrated a number of
interesting trends. There have been yield increases from new
varieties and from crop management. But there has also been
an interaction between breeding and management in that
new varieties respond more to modern management than old
varieties do. Resistance to diseases is an important component
of that interaction.
IT is well accepted that Australian cotton yields have improved
through time. Long term records show that whole of industry
yield during the 1960s was 869 kg lint per hectare (1.5 bales
per acre) and it more than doubled in the 2000s to 1890 kg lint
per hectare (3.4 bales per acre). There are now many examples
of yields in excess of 2800 kg lint per hectare (5.0 bales per acre).
What are the main contributing factors contributing to this yield
increase and how can we further increase yields to keep up with
spiralling costs Long term data from variety trials from across the
industry can help answer this question.
The CSIRO Plant Industry cotton breeding program at Narrabri
was established in 1972 when separate projects operating from
Canberra, Griffith and Kununurra were combined under the
leadership of Dr Norm Thomson. The first variety, Sicot 1, was
released in 1983 and was quickly followed by many varieties over
the following years.
In the 30 years from 1980, a total of 325 experiments with
conventional cotton were grown across all regions in the industry
on commercial farms with commercial management as part of
the evaluation of new breeding material developed from crosses
at Narrabri. The aim has been to identify improved yield and
especially yield combined with better disease resistance, fibre
quality, regional adaptation and stability. Specialised equipment is
required for sowing and harvesting small scale experiments.
The current long term controls and year of release include
Deltapine 16 (1970), Namcala (1978), Sicala V-2 (1994), Sicot
189 (1996), Sicot 71 (2002) and Sicot 75 (2006). Important older
varieties now excluded from experiments because of susceptibility
to Fusarium wilt include Siokra 1-4 (1988), Siokra L22 (1990) and
Siokra V-16 (1998). Deltapine 16 and Namcala were imports from
the US and used as commercial varieties in Australia until local
varieties were developed from 1983.
As new improved varieties are discovered, they replace
older varieties commercially but some older varieties stay in
experiments as long term controls. The large dataset of breeding
experiments provides powerful information to enhance our
research practices and to understand why yield improvements
have been made. Each season, these experiments are sown with
the same seed lot of each breeding line or variety and the same
planter, picker and gin are used, so that measured differences are
due to soil, disease, climate and management at each site.
Figure 1 illustrates the magnitude of adoption of a few major
varieties through time. A single variety may occupy up to 70 per
cent of the conventional area, but generally lasts for less than
10 years before being replaced. Siokra 1-4 (1980s), Sicala V-2
(1990s) and Sicot 71 (2000s) were widely grown commercially;
Siokra L23 and Sicala 40 were also dominant for short periods;
and Sicot 189 and Siokra V-16 were also grown widely in the
1990s.
Experimental design
One of the most important aspects of this dataset analysis
was the use of new complex statistical techniques that take
account of spatial variation in the field due to row effects and
head to tail differences. Such analyses allow more precision with
the yield means of each breeding line and so we can have more
FIGuRE 1: The dynamics of cotton variety
adoption as illustrated by major varieties
grown from 1983 to 2009
Sowing a cotton trial.
Note this figure relates to conventional cotton only – which occupied less than five per cent
of the cotton area by 2010.
20 — The Australian Cottongrower December 2012–January 2013