Final report appendix 6
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- Background
- Objectives
- Methodology
- Procedure
- Crop management
Executive summaryThe Western Australian seed potato industry aims to become a world renowned producer of high quality seed free of pests and diseases. The quality of seed potatoes can be reduced through mechanical damage at harvesting as they are more susceptible to disease as there are more entry points for the disease through the cut surfaces on the tuber. Key areas of the harvesting process that lead to mechanical damage and bruising of tubers in the Western Australian seed system have been identified. The level of damage seen on tubers is variable between growers. Despite the use of different harvesters, five impact points were common amongst all machines. These were (1) sites of tuber drops, and changes in belt (2) direction and (3) speed as well as (4) contact with other potatoes and (5) debris. Impacts ranged from low (< 50 G) to extremely high (> 200 G) during harvesting with the majority in the medium range of 50 – 100 G. Maximum drop heights of 10 - 15 cm are considered the industry standard above which damage is likely to occur but cultivars differ in their susceptibility to bruising. Of all the impacts recorded, the site which consistently recorded the highest impact was the drop from bunker to bin. This site recorded the highest impacts as it had the highest drop point and the greatest number of tubers involved. To reduce this impact and therefore bruising and damage of potatoes it is necessary to change the way this occurs on harvesters by attaching padding or by changes the operator process. Previous research has found that varieties differ in their susceptibility to damage and bruising as is the case in this study. Three varieties were harvested during the study; Atlantic, Bliss and Granola, with Atlantic being highly susceptible to bruising and Granola being tolerant. The knowledge that cultivars differ in susceptibility can be used by farmers to modify their harvesting practices to produce higher quality tubers. Temperature at harvest is a key factor in the level of tuber bruising at or after harvest; generally the lower the tuber temperature the higher the level of bruising. The growers in this study harvested at a range of temperatures between 8.4 °C to 18.4 °C. Management of soil temperature during the crop was also varied with some growers having large variations between their minimum and maximum soil temperatures. Use of soil monitoring units will help aid growers in maintaining a relatively constant soil temperature and therefore minimise bruising. BackgroundOne aim of the Western Australian potato industry is to become a world renowned producer of high quality potato seed due to the state’s freedom of many important potato pests and diseases. For example WA claims area freedom for potato cyst nematode, potato late blight, bacterial wilt and leafminer (Liriomyza huidobrensis). In addition to disease freedom, high quality seed potatoes need to be free from bruising. Bruising and mechanical damage caused during harvesting increases tuber susceptibility to breakdown and can lead to rots in storage and poor seed piece performance. The increased susceptibility to disease is due to the cut surfaces on the tuber providing entry points for pathogens. This is exacerbated if the cut surfaces are not properly cured (Morris et al. 2000). The amount of damage on a tuber is a result of a combination of factors including; cultivar, crop growing conditions, operating conditions at time of harvest and the level of technology used at harvest (Peters 1996). There are two types of potato bruises: black spot and shatter bruise. Black spot bruise involves the damage of the tuber’s cell contents and requires the tuber to be peeled to be visible (Henderson and Bennet 1999). Black spot bruise does not break the skin and results in a blue-black discolouration below the surface (Hyde et al. 1992). Shatter bruise involves damage to cell walls and breaks in the skin that are visible as cracking on the tuber surface (Henderson and Bennet 1999). The tissue around the crack also turns blue-black (Hyde et al. 1992). Shatter bruise can extend to the centre of the tuber and the broken skin is an ideal entry point for diseases (Henderson and Bennet 1999) that lead to deterioration of seed potatoes. Environmental conditions which can affect potato bruising are under-irrigation, or dry soil, which leads to increased incidence of, black spot bruise while over-irrigation, or wet soil, has been associated with increased incidence of both black spot and shatter bruise in tubers. One method used in potato supply chains overseas to measuring physical damage to tubers is the use of an instrumental sphere (IS) (Van Canneyt et al. 2003, Molema et al. 2000a, Hyde et al.1992, Lopresti and Thomson 1998). An IS can identify areas and locations along the supply chain where impacts occur at forces that lead to tuber damage. Identification of high impact locations enables the grower to modify the equipment or the speed at which the harvest or other handling operation occurs to minimise damage to tubers. The IS hasn’t previously be used to measure harvest impacts in WA seed crops under local soil and climatic conditions. We aim to review and analyse the production of seed potatoes in WA with an IS to determine where improved practices may be introduced to improve seed potato quality. ObjectivesOne of the objectives of the project was to review the current seed production systems of the Western Australian potato industry under activity 2.5: Development of suitable training materials on quality seed propagation. The amount of damage on a tuber is a result of a combination of factors including; cultivar, crop growing conditions, operating conditions at time of harvest and the level of technology used at harvest (Peters 1996). The aim of this study was to identify how these factors affect the quality of WA seed potatoes. MethodologySite Location:Crops analysed during this study were grown from Albany and Scott River on the South Coast of WA to Yarloop, north of Harvey as well as Manjimup and Pemberton (Table 4.1). Six seed potato crops were examined (4 Atlantic, 1 Bliss and 1 Granola). Table 4.1: Details of crops investigated in this study including cultivar and crop location with GPS coordinates.
ProcedureDuring harvest the IS was buried in the hill and harvested as a tuber would and all impacts from the soil to the bin stage of the harvesting process were recorded. For those harvesters with a bunker, the bunker drop to bin was performed separately. This information was instantaneously transferred via a sensor to a portable computer. Each harvest run and bunker to bin drop was attempted twenty times for statistical purposes. The information was downloaded onto a desk computer and statistically analysed. Soil moisture and temperature were automatically monitored through the harvest period. Crop managementThe six seed crops were managed by four different farmers and were planted in December 2009 and harvested from March to May 2010 (Table 4.3). Three different models of Grimme harvesters were used for the harvesting (Table 4.3) and each are described in more detail below. Table 4.3: Crop planting date, harvest date and type of harvester used.
The harvesters used in Crops 1 and 5 were Grimme 75 series single row harvesters towed behind a tractor. The plan view of the harvester is seen in Figure 4.3. Sites where tubers change direction and or drop during harvesting are identified as below: First short main web onto diviner web First separator Second separator Bunker filling elevator drop Bin filling from bunker drop 
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