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Thai Journal of Agricultural Science 2010, 43(1): 47-54
The Germination of Corn Weed (Rottboellia cochinchinensis lour clayton) Seed: Induction and Prevention of Germination in Seed C.I. Oyewole* and B.A.O. Ibikunle Department of Crop Production, Faculty of Agriculture, Kogi State University PMB 1008 Anyigba, Kogi State, Nigeria *Corresponding author. Email:
[email protected]
Abstract In Nigeria, Rottboellia cochinchinensis commonly referred to as corn weed has plagued many crops. The control of this weed proved difficult due to the periodic nature of its germination coupled with associated seed dormancy. Trials conducted at the University of Ilorin, Department of Crop Science, Faculty of Agriculture, Kwara State, Nigeria investigated the response of fresh, and old corn weed seeds to various length of soaking (0, 12, 24, 36 and 48 hours) in de-ionized water, and in extracts obtained from the soaking of fresh seeds. The trials also investigated the response of corn weed seeds to various placement methods (horizontal, upright, inverted), and depths (0.5, 2.5, 5.0, 7.0, 7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 cm). Soaking fresh seeds in deionized water led to significant increase in germination. When extracts from the soaking of fresh seeds were used in soaking old seeds for 11-hours, germination was depressed compared to the control treatment. Based on the out comes of the various trials, it was concluded that while flooding of farmland may reduce germination of old corn weed seeds, it will improve germination of fresh seeds. In addition, that, deep plough during land preparation could help reduce corn weed germination. Keywords: Rottboellia cochinchinensis, old seed, fresh seed
Introduction Generally, weeds are usually unwanted plants growing out of place with economic implications (Akobundu, 1982, 1987; Griffin, 1991; DFID, Weeds Project, 2002), which could be competition with farm crops for space, solar radiation, or nutrients, with consequent lowing of expected crop yield or harvest quality with negative implications for monetary return to farmers. It may also be the habouring of crop pests and diseases of farm crops with attendant negative consequences on growth, development and yield, or simply increasing the cost of crop production, due to cost of weed control (Akobundu, 1987; DFID, Weeds Project, 2002), all these cumulating in reduced monetary returns to farmers, either due to yield reduction or increase in
production cost without complimentary increase in returns. Within the challenges of agricultural productivity lies the dominant role of weed pest in preventing the attainment of food security particularly in Nigeria. Besides, the direct effect of weed pest in the form of competition with crops for space, nutrients and solar radiation (Akobundu, 1982, 1987; Griffin, 1991; DFID, Weeds Project, 2002) as highlighted earlier, there is the indirect effects such as cost implication for weed control, and loss of school hours for family members involved in weed control, particularly where manual weeding is common. To surmount the problem of food insecurity in Africa, and Nigeria in particularly, Africa must address, besides other obstacles, the problems associated with weeds
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C.I. Oyewole and B.A.O. Ibikunle
particularly troublesome weed, as corn weed: Rottboellia cochinchinensis. Rottboellia cochinchinensis (sgn. Rottboellia. exaltata) commonly referred to as corn weed (corn grass) itch grass, Guinea fowl grass, jointed grass, prickle grass, rice grass, sugarcane weed, Itchgrass, Kokomagrass, Raoulgrass, Shamvagrass, lisofya, or shamva grass (NAPPO, 2003) has become a major weed in tropical, and sub-tropical regions (Valverde, 2004), where it is recognized among one of the most troublesome weeds of these regions. It is a very competitive weed: 50-plants m-2 have been observed to cause yield reduction of up to 50% in maize (Mercado, 1978). Sharma and Zeloye (1986) observed that when not weeded, corn weed reduced maize yield by 80%, while Akobundu (1981, 1982) observed yield reduction of between of 68-85% in maize and cowpea fields infested with corn weed in Nigeria. In another series of trials in the Philippines, uncontrolled infestations of R. cochinchinensis were found to reduce yields of white food corn by about 50%. Two cultivations using draft animals controlled the weed to some extent, but yields were still reduced by 24% and traditional hand-weeding three times per growing season failed to completely reduce the R. cochinchinensis infestation. In the production of maize, the best weed control was achieved by two mechanical cultivations + hand-weeding and the best economic return was achieved by intercropping maize with mung bean (Fisher et al., 1980). R. cochinchinensis is an aggressive weed under various ecological conditions, in at least 18 crops, including maize, cotton, sesame, sugarcane, soybean and rice in 44 countries. It is also a weed of bananas, cassava, citrus, cowpeas, papayas, groundnut, pineapple, rice, and sorghum in Cuba, Ghana, Jamaica, the Philippines, Trinidad and Venezuela but there is little reference to it in North American cereal crops. It is primarily a weed of warm-season crops in a variety of habitats around the world but can also be found growing along roadsides and in other open, well-drained sites and is an important species in old field succession. The weed does not occur in Canada but it has established in the lower Midwest and Southern US states and is recorded from Mexico (NAPPO, 2003).
Thai Journal of Agricultural Science
Corn weed produces large amount of seeds (NAPPO, 2003), which germinate sporadically in field due to dormancy. Dormancy is reported to be broken within two years, but may extent to four years (Etejere and Ajibola, 1990; NAPPO, 2003). De-husking or exposing sown seed to sunlight was reported to break dormancy in corn weed seed (Pamplona, 1981), while the use of gibberellic acid to break dormancy has been investigated by Etejere and Ajibola (1990). The latter also worked on acid scarification, drying and deterioration of the hull as mean of breaking dormancy in corn weed. While researchers have extensively studied methods of breaking dormancy in corn weed seed (Mercado, 1978; Pamplona and Mercado, 1978; Pamplona, 1981; Etejere, and Ajibola, 1990; Griffin, 1991; Bishundial et al., 1997; Valverde, 2004), research has been scanty on methods of inducing seed dormancy (particularly in old corn weed seeds which will readily germinate), as a mean of checking the spread of the weed. Inducing seed dormancy in corn weed may serve as an important weapon in the control of the weed in infested fields. Innate seed dormancy in most species tends to be gradually lost with time, except in some tree species (Cresswell and Grime 1981; Grime, et al., 1981), often at a rate depending on temperature and moisture content, induced (or secondary) dormancy, in many respects similar to innate dormancy, may subsequently be induced by conditions which signal that the current environment is inappropriate for germination (Cresswell and Grime 1981; Grime et al., 1981). Enforced dormancy may be temporarily imposed by conditions which again appear to play a role in ensuring that the seed only germinates when and where it is required (Cresswell and Grime, 1981; Grime et al., 1981). In the case of corn weed this can serve as an important weapon in its control; employing the innate growth inhibitor in fresh seed in the suppression of germination in those seeds that would have readily germinated, in this case, old corn weed seeds. In view of the danger posed by corn weed, and the difficulties encountered in its control (NAPPO. 2003), coupled with the call for reduced herbicidal usage, as a result of the attendant environmental pollution, disruption, secondary pest outbreaks, pesticide resistance, gross wildlife and public health
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Germination of corn weed seed
effect (Gutierrez, 1987), this research focused on understanding the various factors (seed placement, depth of seeding, dehusking of seed, seed wounding, soaking in de-ionized water and in fresh seed extracts) which may limit seed germination, emergent, establishment and growth with a view to controlling the weed; as understanding the weed is an essential step in its control. As a mean to employing flooding in the control of corn weed, this research investigated the effect of seed soaking on corn weed seed germination; effects of placement and sowing depth on seed germination and emergence, as a mean to employing tillage operations in corn weed eradication; effect of plant population on tiller formation, as a mean to employing cultural practices; while other treatments considered include: shade effect on plant development, de-husking and injuring corn weed seeds before sowing. What factors informed the selection of these treatments? It has been observed that at any one time it is common for there to be more dormant seeds in the soil waiting for appropriate conditions than there are growing plants (Cresswell and Grime, 1981; Grime et al., 1981). The question is what happens if these reserves are flooded or ploughed deep into the soil? This question informed the investigation of seed soaking and seeding depths as means of corn weed control. Furthermore, it would seem that many species have evolved dormancy mechanisms which avoid problems. The seed needs to be able to respond to environmental factors that signal when it is at or near the soil surface and there seem to be two major environmental factors which many species use as indicators -light and alternating temperatures; and in most cases the seeds respond to both (Cresswell and Grime, 1981; Grime et al., 1981). Light is obviously only present at or near the soil surface; and diurnal temperature alternations have a maximum amplitude (or diurnal range) at the soil surface: the range rapidly diminishes with depth in the soil profile. The focus on seeding depth was meant to explore this principle. In addition, small seeds, as in corn weed, only contain small food reserves, thus requires small amount of seedling growth before the seedling needs to start photosynthesizing. Germination more than a few centimeters below the soil surface or beneath dense vegetation could lead to seedling
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destruction (Cresswell and Grime, 1981; Grime et al., 1981), this realization informed the study of shade effect. Another question that came to mind was, does the seed contain enough food reserve to emerge from the studied depths and at what depth will it fail to emerge? These were the questions the research set out to explore and formed the bases for the selection of the treatments. Materials and Methods Series of experiments were conducted with the view to investigating all limiting factors to corn weed germination as means to its control. All trials were conducted at Faculty of Agriculture, University of Ilorin, Ilorin, Kwara State, Nigeria. Old corn weed seeds used in these experiments were collected two years before the commencement of the experiment from fallow popcorn field in Bellah, Asa Local Government area of Kwara State, Nigeria and were stored at ambient temperature. Based on available literature, dormancy would have been broken after such storage, thus these seeds should readily germinate on sowing. Fresh corn weed seeds were collected when required from abandoned farm lands at the permanent site of the University. The sowing medium, dark perforated plastic buckets were filled with sterilized soils collected from advanced fallow farmlands to within 2.5-cm of the brim to allow for watering, and the plants were liberally fertilized (NPK 15:15:15). The plastic buckets were kept in Faculty’s pavilion shade, and watered daily. Experiment 1: Seed Soaking in De-ionized Water This trial was meant to investigate the effect of flooding of farmland on germination of old (dehusked and undehusked) and fresh corn weed seeds. The trial investigated the response of fresh and old (dehusked and undehusked) corn weed seeds to various length of soaking (0, 12, 24, 36 and 48 hours) in de-ionized water. Five samples each of old (dehusked and undehusked) and fresh corn weed seeds were soaked in de-ionized water (for 0, 12, 24, 36 and 48 hours), the soaked seeds were removed after the stipulated time period as in the treatment and sown at 0.5 cm depth in plastic buckets containing heat sterilized soils.
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C.I. Oyewole and B.A.O. Ibikunle
Experiment 2: Seed Soaking in Fresh Seed Extracts This trial was aimed at investigating the possibility of using the germination inhibitor in fresh corn weed seed to depress germination in old corn weed seed. It was assumed that the inability of freshly harvested corn weed seeds to germinate was as a result of growth inhibitor resident in the husk, as previous experiments revealed that germination of freshly harvested seeds improved with dehusking. The trial involved weighing 20 g of five batches of fresh seeds into clean beakers containing 50 mL of de-ionized water for 0, 12, 24, 36 and 48 hours. At the end of the soaking period, extracts obtained from soaking of these fresh corn weed seeds were used in soaking batches of 50-old seeds for 11 hours after which the seeds were sown ten seeds per bucket. Previous experimental observations made on water absorption capacity of corn weed seeds revealed that seeds had attained maximum water absorption within 5 hours of soaking. This observation informed soaking old corn weed seeds for 11 hours; about twice the length of time required to reach maximum water absorption level. Experiment 3: Placement Effect on Germination The following placement methods were investigated: (1) horizontal - when seed was sown on its cylindrical side, (2) inverted - when seed was sown with the depressed (cup) end downwards and the peg upward and, (3) upright - when seed was sown with the depressed end upward, and the peg downward. To ensure the placements, sowing buckets were filled with top soil to appropriate level and ten seeds placed as in the treatment and covered with more top soil to 0.5 cm depth. Experiment 4: Depth Effect on Germination Depths investigated were 0.5, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 cm. Ten seeds of corn weed were sown per treatment at the appropriate depths. Data Analysis All data were analyzed as described for RCBD (Gomez and Gomez, 1984). Where treatments were found to be statistically significant (p
