GROW OUT TEST AND DETERMINATION OF PHYSICAL CHARACTERISTICS OF SEED OF RICE LANDRACES

The study was attempted with an objective to check the purity of commonly used farmer’s rice seed stock. Assessment of varietal purity of collected 76 rice genotypes showed that there was a variation among the genotypes for varietal purity. Thirty-two genotypes showed 100% varietal purity and forty-four genotypes were contaminated with different types of offtypes. The lowest varietal purity was observed in Lal gotal (74.67%). Grain dimension and 1000 seed weight were measured as important physical characteristics of seed to identify varietal purity.


Introduction
A large number of the farmers of Bangladesh are adopted with local landraces and they are cultivating these for long period with traditional cultural practices.As a result, the yield of those varieties is decreasing due to genetic impurities through mechanical mixtures, incorporating with off-types or volunteer plants, natural outcrossing, mutations etc.Samples of cultivars from farmer's fields are rarely homogenous in genetic composition.They contain varying degrees of differences in morphological or physiological aspects, some obvious to the eye while some others are not.Generally, a farmer's variety can be differentiated into two or more subpopulations that are distinct in one or more recognizable traits (Chang, 1976).Landraces are generally low yielding, but have high yield stability and resistance against many biotic and abiotic stresses.Conventionally grow out test (GOT) is used to assay the varietal purity of rice seed lots on a representative sample of the seeds (Moorthy et al., 2011, Naresh et al., 2009, Sundaram et al., 2008, Sang et al., 2006).In GOT, plants are grown up to maturity to identify the off-types through assessing several morphological and floral characteristics that distinguish the genotypes (Yashitola et al., 2002).GOT is time consuming (takes one full growing season for completion), space demanding and often does not allow the unequivocal identification of genotypes.The molecular markers are of great importance for rapid assessment seed purity (Yashitola et al., 2002, Antonova et al., 2006and Pallavi et al., 2011).Rajendrakumar et al. (2007) used molecular markers for detection of contaminant in CMS seed stocks of rice and confirm result based on observation recorded in GOT field.Therefore, this experiment was conducted to evaluate the varietal purity through GOT and important seed physical characters were determined according to IRRI guidelines.

Materials and Methods
The experiment was conducted at the experimental farm of Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, during July 2011 to December 2012.Geographically the experimental area is located at 24 0 75 N latitude and 90 0 5 E longitudes at the elevation of 18 m above the sea level.The field was medium high land.The soil of the experimental site belonging under the agro-ecological zone of Old Brahmaputra Floodplain (AEZ-9).The experimental field area was under sub-tropical climates characterized by heavy rainfall during the month of April to September and scanty rainfall during October to March.Fifty four rice landraces (i.e.Dudh kalam, Hati bajore, Malagoti, Kuchra, Enghi, Kajol shail, Hogla, Jamai naru, Hari, Dakh shail, Moina moti, Marish shail, Patnai, Bhute shallot, Kute patnai, Mohini shallot, Moghai balam, Sada gotal, Khak shail, Mohime, Holde gotal, Jota balam, Tilek kuchi, Rani Shalot, Kathi goccha, Bashful balam,

Grow out test (GOT)
Data were recorded on off-types from per plot in each block, which were not identified at earlier during seed processing after collection.Among the studied characters, number of off-types meter -2 and types of off-types meter -2 were recorded in the field and the remaining two characters were calculated and recorded in the laboratory, which were as follows:

Number of off-types meter -2
By regular field visits, off-types were identified in each plots and marking of off-types with tag was done on a regular basis.Panicles of the off-types were covered with bags made of glossy papers to avoid further out crossing in order to maintain genetic purity of the rice genotypes of the plot.Selection criteria for off-types at different stages of crops followed in this experiment is shown in Table 1.The land was free from volunteer plants.

Types of off-types meter -2
At harvesting stage, off-types were classified into different types based on the plant height, difference in seed size, shape, presence or absence of awns and seed coat color.Similarities of these characters among the off-types were considered as same off-type genotypes in this experiment.
Percent (%) off-types meter -2 = (Number of off-types meter -2 ⁄ Number of total plant meter -2 ) x 100 In this experiment, Number of total plant meter -2 was 25 in each case.

Measurement of physical characteristics rice seed
Grain dimensions (length-width ratio) were measured according to the standard rice grain size and shape scale followed in IRRI and is shown in Tables 2& 3. Table 2

Grow out test (GOT)
The analysis of variance for evaluation of varietal purity of 76 rice landraces is shown in Table 4. Analysis of variance showed that there were significant variations among the genotypes for all the characters studied.This indicates that there was a variation among the genotypes for varietal purity.In Table 5 it was found that number of off-types meter -2 ranged from 0 to 6.33.Out of 76 genotypes, the highest number of off-type was observed in Lal gotal, which was closely followed, by Jota balam, Mura bajal and Mohime.Thirtytwo genotypes were free from off-types.The range of types of off-types meter -2 was 0 to 5 and the mean value for this trait is 1.20.The highest types of off-types were recorded in the plot of Lal gotal followed by Mura bajal, Jota balam and Mohime.

Measurement of physical characteristics of rice seed
In case of grain size, seven genotypes were categorized as long; fifty-five as medium and fourteenth as short grain ( With respect to shape, eight rice grains were evaluated as slender as the grain length width ratio was more than 3.0; fifty seven rice grains were considered as medium as the values were existed between 2.1 and 3.0; and eleven rice grains were estimated as bold as GLWR values were existed between 1.1 and 2.0 (Table 7).

Fig. 1 .
Fig. 1.Different types of off-types found during varietal purification of the landrace MohimeThe highest percent (%) of off-types was recorded in Lal gotal (25.33%) followed by Jota balam (24%), Mura bajal (24%) and Mohime (21.33%).The range for this trait was 0 to 25.33.In this experiment, thirty-two genotypes showed 100% varietal purity and forty-four genotypes were contaminated with different types of off-types.The lowest varietal purity was observed in Lal gotal (74.67%).This indicates that a majority percent of landraces are in a process of varietal deterioration.

Table 1 .
Off-type selection criteria followed in the experiment . Size classification of rice grains (Source: www.irri.org)

Table 3 .
Shape classification of rice grains

Table 4 .
Analysis of variance for evaluation of varietal purity of 76 rice genotypes ** indicates significant at 0.01 probability

Table 7 .
Shape classification of 76 rice grainsThe range of 1000-grain weight was 11.28g to 31.93 g.Highest 1000-grain was obtained from Mota aman (31.93 g) and the lowest was observed in Chinishail (11.28 g).The mean value for this trait is 24.23 g.Seed physical characteristics of these genotypes are presented in Table8.In future, varietal purity of these genotypes could be determined through comparing with this data.Although we have now large number of HYV rice varieties, farmers do special affinity to landraces and substantial conservation of diverse landraces of rice in Bangladesh has continued since ancient times.The genuineness of the variety is one of the most important characteristics of good quality seed.A mixture of varieties in a field may significantly diminish the value of the crop due to poor yield, downgrading and reduce milling yield.Genetic purity test is done to verify any deviation from genuineness of the variety during its multiplications.The present study showed that conventional GOT test is an effective method of varietal purity test although morphological markers are time consuming and are environmental dependence.