Template:Chapters 7.2
7.2 - Constant visual inspection for sick plants
Nick Moroz, University of Guelph,Canada
Introduction to Careful Seed Selection and Methods
The importance of high seed quality for achieving a productive harvest cannot be overstated, especially over multiple harvest seasons. This paper will discuss what to look for in seed quality as well as describe methods on how to efficiently separate poor quality seeds from high quality seeds. In general, spotted or discoloured seeds mean diseased or unhealthy seeds (Rural Development Academy, 2006). In order to increase the yields of many grain crops globally, simple and low-cost solutions for seed quality control should be considered for farmers in developing countries (CSISA & IRRI, 2014; Mathur, Talukder, Veena, & Mortensen, 2004). The major method this paper will discuss is the Water Floatation Technique, a simple strategy that can be used to rid seed stocks or planting materials of infected or diseased seeds through separation. There are various techniques that can increase crop production by separating diseased seeds from healthy ones, including careful visual inspection of seeds or planting material and manual removal of discoloured or spotted seeds from the stock, hereby referred to as careful seed-selection (Rural Development Academy, 2006). One study in Bangladesh showed that careful seed-selection increased rice germination from 66% to 87%, increased seed quality and yields, and reduced disease and pest infestations in the local soils (Mathur et al., 2004). Similarly, the Water Floatation Technique can rapidly separate healthy, properly coloured seeds with those that are discoloured, malformed, and infected. Water floatation techniques assist in the rapid removal of sick or infected seeds, reducing the workload that is required in careful seed-selection by hand. Many farmers are currently employing water floatation techniques or careful seed inspection techniques but there are more who could benefit from these methods.
Why choosing the best seeds matters
Farmers tend to select the best seeds over time and use them in the following seasons. Sometimes there are contaminated seeds that continue to be missed in the seed stock and unfortunately can be planted in following planting seasons, reducing yields and spreading infection (Mathur et al., 2004). This paper offers techniques to remove the contaminated seeds and maintain a fresh stockpile of healthy seeds for future planting, increasing seed germination and boosting yields over multiple years. In order to be confident in seed quality farmers must buy certified seeds or produce their own good seeds, and they should be constantly selecting for the healthy seeds, removing any infected seeds through water floatation or careful seed-selection (CSISA & IRRI, 2014). If a farmer is using their own seeds, the seeds should be clean and containing no weed seed, soil, or stones (CSISA & IRRI, 2014). Seeds must also be pure (only one variety), and healthy, meaning they are the same color with fully filled grains and free of cracks (CSISA & IRRI, 2014).
Supply of certified seeds is extremely limited in most developing countries, with more than 95% of the seeds used in these countries coming from the informal seed sector, mostly from farmers’ own saved grains (Mathur et al., 2004). Yields can be low due to diseased seeds that result in poor germination rates and ultimately sick, unproductive crops (Mathur et al., 2004). A crop management project that started in Bangladesh in 1998 showed that rice seed samples collected from local farmers were infected by bacteria, fungi, or disease and resulted in poor germination rates (Mathur et al., 2004). The seeds that were causing low germination rates were shown to be those seeds that visually looked discoloured or spotted (Mathur et al., 2004). After careful seed-selection and manual removal of these spotted seeds, germination rates of the rice seed increased to rates of 87% on average compared to 66% on average in the original (or unaltered) seed stock samples (Mathur et al., 2004). For a thorough explanation of the methods of this study see Mathur et al. (2004). Mathur et al. (2004) results show that rice seed samples that contained the discoloured or spotted seeds had low germination and poor looking seedlings compared to the carefully selected seeds (see Table 1.0). Discolouration and spots on rice seeds are coloured due to infectious fungi and bacterial infections (Mathur et al., 2004; Singh & Rao, 1977; Rural Development Academy, 2009), and the germination of such infected seeds is diminished. Thus, this paper proposes that simple manual removal of seeds through careful selection or by water flotation techniques will greatly benefit farmers by improving their seed stores and crop health and productivity
Adapted from Mather et al., 2004:. Each sample of seeds was mixed using a Boerner divider, as required to satisfy the International Rules for Seed Testing (Mather et al., 2004). A third of the Original Stock (OS) of each sample (500g of seeds from Tangail district) was kept while the remaining two thirds OS was cleaned by hand. Using a seed spatula and forceps discoloured and spotted seeds (DSS) were removed (Mather et al., 2004). These remaining non-spotted and non-discoloured seeds were put into the category Healthy Sorted Seeds (HSS). Next, sub-samples were taken from these three categories of seeds (OS, HSS, and DSS) and germination rates were tested via the Between Paper method at 25°C and 30°C. (Mather et al., 2004).
Grafting allows for individual fruit farmers to respond to market changes faster than if they were to plant a young tree, since fruit will be produced quicker from the combination of mature rootstock and scion than from a younger tree (Hart, 2005). Consequently, there remains a stronger possibility that this individual will have access to larger markets and higher asking prices for in-demand fruits and vegetables.
Some trees, such as the Baobob tree from the Sahel countries of Africa, are grafted quite easily, with success rates ranging from 80-95% (Maranz, 2008). However, this is not consistent across all species, and does not account for the ‘learning curve’ in practicing proper technique. Maranz (2008) notes that ‘exotic’ varieties of Baobob (those from other Sahel countries) have superior nutritional benefits, and determines that grafting represents an interesting possibility for developing a market for the new varieties, since the local variety has far superior basal diameter, tree height, and resistance to termites. Assah (2011) details the possibility of an emerging market for three novel Alanblackia species in Africa for its nutritive, medicinal, cosmetic, and detergent properties. These species could be grafted onto locally available rootstock for local production to take place. Mudge (2009) details the grafting of Ceara rubber tree onto a cassava rootstock, for the purpose of invigorating the rootstock. The resulting yield of cassava tubers was increased by 30-100% depending on the combination of species.
Critical analysis
Grafting at a large scale is labour intensive, and does require some training. The success rate of grafting is highly variable depending on species; research should be performed on the specific species to determine average success rates, or a test plot should be initiated (Mudge, 2009). There is an ongoing debate about the possibility of the transference of genetic material from scion to rootstock and how this affects the ‘heritage’ of traditional varieties (Mudge, 2009).
Practical tips
The University of Minnesota has a comprehensive manual on grafting, including timing, species selection, and materials needed.
The University of Arizona publishes free ‘how-to’ videos on vegetable grafting. While limited to tomatoes, curcubits and eggplants, many of the principles remain the same.
Usefull Images
References
Asaah, E., Tchoundjeu, Z., Ngahane, W., Tsobeng, A., Kouodiekong, L., Jamnadass, R., & Simons, A. (2011). Allanblackia floribunda: A new oil tree crop for africa: Amenability to grafting. New Forests, 41(3), 389-398. Hart, T., & Burgess, R. (2005). Grafting keeps farmer in the export market. Appropriate Technology, 32(3), 13-14. Retrieved from http://search.proquest.com/docview/200037126?accountid=11233 Kudo, & Harada, T. (2007). A graft-transmissible RNA from tomato rootstock changes leaf morphology of potato scion. HortScience : A Publication of the American Society for Horticultural Science., 42(2), 225-226. Maranz, S., Niang, A., Kalinganire, A., Konaté, D., & Kaya, B. (2008). Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting. Agroforestry Systems, 72(3), 231-239. Mudge, K., Janick, J., Scofield, S., & Goldschmidt, E. E. (2009). A history of grafting. Horticultural Reviews.,437-493.