Effect of infestation with acaridid mite, Tyrophagus putrescentiae (Schrank) on germination rate of maize grains

The infestation of maize grains with the harmful acarid mite, T. putrescentiae at the laboratory was conducted after 3, 6 and 9 months. The number of normal, abnormal and analyzed maize grains was conducted. The infestation of maize grains with the harmful acarid mite, T. putrescentiae at the laboratory was conducted after 3, 6 and 9 months. The numbers of normal, abnormal and analyzed maize grains were conducted for 50 grains. Generally, it was noticed that the number of normal maize grains increased with decreasing the number of mites infested to grains and also with decreasing the time of infestation, while the number of abnormal maize grains increased with increasing the number of infestation mites and also with increasing the time of exposure to mites.


INTRODUCTION
The mites, being important pests of stored grains, are responsible of both qualitative and quantitative losses in stored grains.These mites feed on embryo thus resulting in germination loss in the grains (Zakhavatkin, 1941) along with deterioration in quality of seed as well as flour prepared from the infested grains which also make it unsuitable for milling and unpalatable for livestock (Wilkin and Stables, 1985).Many commercial farmers are unaware of the damage and losses caused by the stored grain mites mainly due to their minute size (Palyvos and Emmanouel, 2006).The direct damage of mites to stored grains is through contamination and penetration in to seeds/embryo, consumption of the grain germ and some extent, the endosperm (Parkinson, 1990) which consequently decrease the vitality and germination capability of the seeds.The grain becomes useless for seed (Zdarkova, 1996) or brewing purposes and unacceptable to the miller (Solomon, 1946).The cereal, grains and stored products are liable to be attacked not only by insects, but also by mites, which either free living granaries, fungivorous and saprophagous or parasitic or predator on other mites and insects.Mites associated with stored products are of great economic importance, causing injury by feeding and its contamination with dead bodies and excreta makes these sources of food undesirable in addition to its digestion troubles.Damage by insects, fungi, and sprouting cause hundreds of millions of dollars of economic losses to grain producers, merchandisers, and processors each year (Harein and Meronuck, 1995).Haq and Afzal (2007) in Pakistan decided that mites infested grains undergo a series of changes in their chemical composition and affecting the germination capacity, flour prepared from contamination grains is more acidic, fusty smell and bitter taste.In their studies about the relation between the stored product grains and mites on germination of certain cereals.Ashfaq et al. (1996) and Zdarkova (1996) mentioned that the stored grain and stored products mites decrease the germination percentage of cereals and also infest and damage other food stuffs as cheese, flour, seed, bulbs, tubers and dried fruits of all kinds and decaying material and other such items are the main factors for habitation of these mites.Ramzan et al. (1991) noticed that damage variation in different wheat was from 17.4 to 45.0 % after one year of storage and the weight lost of maize and maize due to mite infestation differed according to infestation where it consumed the highest amount of grains which in turn affected on the germination of these grains.

MATERIALS AND METHODS
Germ inability was determined by using grains of maize (50 grains).Folded towels of each treatment were maintained in an incubator at 25-30 ºC.A relative humidity of 75-85 % was maintained in the incubator along the period of germination test.The folded towels were also moistened continuously.They needed moisture to the grains at all times.The number of germination grains was recorded after 3, 6 and 9 months of infestation.The number of used mites in infestation was 50, 100, 200 and 300 of Tyrophagus putrescentiae adult stage which was already reared in the laboratory conditions on some yeast granules.For calculating the germination percentage one hundred grains of each stored commodity were placed and soaked on blotting paper in the Petri dish.Each treatment was repeated six times.After a period of 72 hours, the number of germinated seeds in each Petri dish was counted and germination percentage was estimated by the following formula: Germination % = Number of germinate grains x 100 Total No. of grains soaked in each Petri dish

RESULTS AND DISCUSSION
Maize (Zea mays L.) is one of the most nutritional crops and proper storage of seeds continues to be a challenge for subsistence farmers.In this study, the infestation of maize grains with the harmful acarid mite, T. putrescentiae at the laboratory was conducted after 3, 6 and 9 months.The number of normal and abnormal maize grains was conducted.

A. After 3 months:
The obtained data in Table (1) denoted that the number of abnormal and analyzed grains was increased by increasing the number of used T. putrescentiae.On the other hand, the number of normal grains increased with decreasing the number of mite's infestation.Data in Tables (1 and 2) indicated that the number of normal maize grains after 3 months increased significantly with decreasing the number of mite infested these grains, where the number was 46.5 normal grains but abnormal and analyzed grains was 3.5 grains, respectively.However, in case of 300 mite individuals, the normal of maize grains were 30.5 mites but abnormal and analyzed grains recorded 19.5 grains.

B. After 6 months:
As shown in Table (1) the number of normal grains were increased with decreasing the number of infested mites which decreased gradually by increasing the number of T. putrescentiae reaching to 28.5 normal grains when exposed to 300 mite individuals.On the other hand, the highest number of abnormal maize grains (21.5) was noticed when the grains exposed to 300 mite individuals.However, the same trend of observation was recorded in case of analyzed maize grains where the highest number of analyzed grains was obtained when 300 mites introduced.From the obtained data, it was denoted that there were highly significant differences between the number of abnormal and analyzed maize grains and the number of introduced mites, Table (2).

C. After 9 months:
The tabulated data in Tables (1 and 2) showed that the number of obtained normal maize grains significantly decreased with increasing the number of T. putrescentiae where the number was reached to the highest healthy grains 42.0 one with introducing 50 mites only, the number decreased to reach to 26.5 grains with 300 mites of T. putrescentiae.The highest number of abnormal and analyzed maize grains after infestation with these harmful mites reached to the highest level of damage when the grains infested with 300 mites also where the number of the abnormal and analyzed was 23.5 grains wheat that was infested by each of 3 species of mites, Lepidoglyphus destructor (Schrank), Acarus farris (Oudemans), and Aeroglyphus robustus Banks studied by White et al. (1979) to determine the effects of mites on the quality of wheat.L. destructor infestation of the grain led to significantly lower fat acidity values (P<0.01) and significantly slower loss of seed germination (P<0.05)than in the noninfested wheat.The infestation of maize grains with the harmful acarid mite, T. putrescentiae at the laboratory was conducted after 3, 6 and 9 months.The numbers of normal, abnormal and analyzed maize grains were conducted for 50 grains.Generally, it was noticed that the number of normal maize grains increased with decreasing the number of mites infested to grains and also with decreasing the time of infestation, while the number of abnormal maize grains increased with increasing the number of infestation mites and also with increasing the time of exposure to mites.In this line, Bashir (2010) mentioned that the mites cause both quantitative and qualitative losses.As a result of their infestation, along with weight reduction, the grain losses the viability.Also, according to Canadian Grain Commission (2010), the grain mites Tyrophagus putrescentiae attacks the germ (embryo) of seeds, which reduces germination, and spreads fungi (moulds), which are also eaten.The present studies can be compared with those of Ashfaq et al. (1995) who revealed 15-20 % germination loss in grains of wheat, maize and mung collected from Mansehra District due to mite pests after three months of storage.Generally and based on the obtained results it can be concluded that T. putrescentiae mite is mainly responsible for the germination loss in the stored maize grains.

Table 1 :
Effect of Tyrophagus putrescentiae infestation on the germination of maize grains (50) without washing after different exposure times.

Table 2 :
Effect of storage time and number of T. putrescentiae on the germination of maize grains.