Sugarcane cultivars

species) with high levels of disease resistance, adaptability and stress tolerance (Screenivasan et al.

1987).

All the main sugar producing countries have embarked on sophisticated sugarcane breeding, selection and evaluation programs. The time from making an initial cross to commercialization is more than ten years in Australia (Cox et al. 2000) and between 11 and 16 years in South Africa (Meyer et al. 2010) and involves considerable human and financial resources.

Development of new cultivars involves two important stages. The first is the generation of variability and genetic combination for the important traits to be incorporated into a new cultivar. The second stage is the identification of genotype that combines the important traits required for commercial cultivars. After this the selected genotypes are tested to determine the expression of the genes that control these traits.

The considerable investment in breeding and selection programs is protected by Plant Breeders Rights (PBR). In some instances there is a requirement to pay royalties for new cultivars that are grown commercially. Contracts between the grower and the research institute are sometimes required to allow for the commercial use of certain cultivars.

Diseases that threatened the viability of the sugar industry resulted in many of the governments legislating for both control of production and cultivar use.

Sugar production is largely under government control and the Sugar Act and Regulations determine how industries are regulated and operated. It is normal for the Sugar Act to be more general and for the Regulations to apply the operating procedures. However, in some countries (e.g. Kenya) the Sugar Act is very detailed and specific in laying down what can and cannot be done. In addition governments are responsible for plant quarantine and phytosanitary requirements as well as controls over import and export of cultivars.

The main industries are developing programs to help select the most profitable cultivars for use based on the classification of the most desirable traits (e.g. Inman-Bamber and Stead 1990). There is also broader based research (Bezuidenhout et al .2007) to look at agroclimatic and hydrological responses, which help support regional decision making strategies on cultivar, etc. Landell et al.

(2009) developed a matrix for central-south Brazil for selecting cultivars on the basis of production, soil type, time of harvest and stage of cultivar testing. Batistini Brunoro and Moreira Leite (1999) used linear programming of production versus costs, including transport, to design sugarcane production policy based on cultivar choice. Ramburan et al. (2010) have developed a cultivar

selection decision support system based on genotype x environment analysis and system evaluation.

Most major producing countries publish literature on cultivar selection, performance and

management. The 26 sugarcane cultivars in Brazil are described by Zimback and Figueiredo (1990) and cover the cultivars produced by the Institute of Agronomy of Campinas (IAC) and for SP and RB cultivars used by Planalsucar. Ramburan et al. (2007) provided an overview of the released cultivars in South Africa. Manuals (e.g. India, Srivastava et al. (1998)) or Information Sheets (South Africa, SASRI) and the internet (Queensland cultivars) provide specific information to the growers they serve.

1.6.3 Sugarcane taxonomy

Sugarcane belongs to the genus Saccharum L of the tribe Andropogonae in the grass family Poaceae, which includes Sorghum and Zea. The Saccharum genus comprises six species, S. spontaneum, S.

officinarum, S. robustum, S. edule, S. barbari and S. sinense (D’Hont et al. 1996). The taxonomy and phylogeny of the five interbreeding genera share common characteristics and are known as the Saccharum complex (Daniels and Roach 1987). There are high levels of polyploidy and frequently unbalanced numbers of chromosomes (aneuploidy) making it difficult to determine taxonomy (Daniels and Roach 1987; Screenivasan et al. 1987).

1.6.4 Centers of origin

New Guinea 6 000 BC is the first record of S. officinarum, a cultivated species not known in the wild (Screenivasan et al. 1987), which resulted from complex introgression between S. spontaneum, Eriathus arundinaceus and Miscanthus sinensis. (Daniels and Roach 1987). This noble cane was spread along human migration routes throughout Southeast Asia, India and the Pacific, hybridizing with wild sugarcanes, and ultimately producing ‘thin’ canes. Sugarcane reached the Mediterranean between 600 and 1 400 AD, spreading into Egypt, Syria, Crete, Greece and Spain; then down into West Africa and subsequently across into Central and South America. The centre of origin of S.

officinarum is probably Polynesia with modern central diversity in Papua New Guinea and Irian Jaya (Indonesia).

S. spontaneum probably evolved in southern Asia. This cultivar accumulates no sugar and is a highly polymorphic species with high levels of disease resistance, adaptability and stress tolerance

(Screenivasan 1987). It is widely grown from 8° S to 40° N and extends across three vast geographical zones (Pursglove 1972; Daniels and Roach 1987; Tai and Miller (2001).

1.6.5 Hybridization

Modern cultivars are based on 20 S. officinarum and less than 10 S. spontaneum derivatives (Roach 1995). Genome in situ hybridization (GISH) showed approximately 15 to 20 % S. spontaneum chromosomes and less than 5 % translocated or recombinant chromosomes (D’Hont et al. 1996;

Cuadrado et al. 2004). In Australia most cultivars can be traced to POJ 2878 (the ‘Java Wonderclone’).

The modern cultivars have many different and often specific traits, which give them advantage over the older cultivars. Primarily, the cultivar must be high yielding with good ratooning ability. The cultivar must also have desirable agronomic traits, tolerance to diseases and insect pests and fit into the management system. The cultivar must also be adapted to the local climate and soil

environment.

A cultivar might start out well but suddenly succumb to a change in insect pest or disease pressure or to a new pest or disease. The cultivar is part of a diverse changing biological system, and climate change could well have a direct impact on cultivar performance as well as on insect pest and disease pressure in the future.

1.6.6 Diseases

Changes in cultivar due to diseases are well illustrated by Bailey (1995) in South Africa. Cultivars were subject to smut, which was identified in 1877 followed by Mosaic in 1910 to 1920s. Streak occurred in the 1930s and rust and RSD in the 1940s. Leaf scald became a threat in the 1970s and RSD was widespread in the 1980s. In the 1990s two new viruses (SCBV and SCMMV, a retrovirus) emerged.

RSD in the 1940s resulted in Co281 being replaced by NCo310, which later succumbed to high levels of smut, and NCo376 was the next victim to succumb to smut in the hotter northern areas. NCo376 and NCo293 were both infected with mosaic in the cooler areas. The proportion of NCo376, once the major cultivar, has fallen to 3.9 % in South Africa, 11 % on Triangle Estate in Zimbabwe and 24 % on the two estates in Tanzania.

The diseases of sugarcane that cause yield losses in Australia (Frison and Putter 1993; McLeod et al.

1999; Croft et al. 2000) have impacted on cultivar choice. The most widely grown cultivar, Q124, was severely damaged by orange rust (Apan et al. 2003). This led to the development of more resistant cultivars. Risk and productivity were assessed and a matrix was produced to assist growers reduce risk in the future (Wilcox and Croft 2004). Other cultivars (e.g. Q173 and Q182) have also since succumbed to the disease (Anon 2005a). Smut was first recorded in Australia in 1998 in the Ord river area of Western Australia. The outbreak was first controlled, but in 2006 it spread to Childers in Queensland and has continued to spread. Control of smut has been based on growing resistant cultivars (e.g. Q177, Q200, Q208, KQ228 and QS94-2329). Soil type interacts with both yield and resistance (Watson 2007).

1.6.7 Pests

Pests have also caused havoc in different parts of the world. Cane grubs are a major pest affecting the Australian sugar industry and cost the industry millions of dollars per year in yield loss and control costs. Control measures are unsatisfactory, and reliance is being placed on breeding with some success (Allsopp et al. 2003). Recently genetic engineering of sugarcane for resistance to cane grubs has been initiated (CRC SIIB 2006).

Samson et al.(2004) reported evidence of an effect of cultivar on soldier fly. Cultivar Q138 produced lower pupations of smaller larvae, which also took longer to mature compared with the same pest on Q135.

Agnew (1997) lists 28 pests affecting sugarcane in Australia. Many are rare or sporadic pests not requiring control. Leslie (2004) provides a comprehensive overview of sugarcane pests worldwide and control involving the use of resistant cultivars.

The major pest affecting sugarcane in South Africa is the stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae) (eldana), which has largely been addressed by field hygiene, reduced carry- over and resistant cultivars.

Nematodes cause yield loss, particularly on poor sandy soils when the crop is under stress and moisture is limiting. There are a wide range of nematodes and control is based on cultural and chemical control methods as well as cultivar resistance (Cadet and Spaull 2005).

The use of resistant cultivars is particularly useful, as it reduces the use of harmful chemicals which can disturb the balance of nature and result in other pests becoming a problem. Integrated Pest Management (IPM) strategies are continuously being developed on the basis of holistic

agroecosystem interactions (e.g. Conglong and Rutherford 2009) and are wide ranging, from habitat management to specific high technology such as Sterile Insect Technology (SIT). IPM requires a full understanding of all the pest, predator, habitat, climate and management interactions as well as an understanding of available modern technology such as SIT.

Cultivar adoption patterns have been studied in the Australian sugar industry (Mordocco et al.

2007), and showed generally good adoption of new cultivars.