Kale is one of the favorite cool-weather crops that are mostly planted by many gardeners. The great qualities that kales have include delicious, nutritious, and versatile. Kale has the capability of growing in any climate zone (Vanderlinden). Some of the popular varieties of kale include the Red Russian, which has light purplish stalks, grayish-green leaves, and purplish veins. The Red Russian variety is the most delicious variety. The other variety is the Lacinato, which is also referred to as dinosaur kale, cavolo Nero or Toscano Kale (Rutherford-Fortunati). This variety is extremely hardy with the leaves getting very tough when they grow to be too large. The other variety is the winterbor, which is a curly kale that had deep green and ruffled leaves (Vanderlinden).
In the farming of kale, the most pests that are known to infest the crop are the cabbage worm. The worms are small, green in color and are the Cabbage White butterfly larvae. They usually eat holes in the kale leaves leading to the destruction of the harvest. Control of the larvae can be done through cultural, chemical or biological means. The cultural means include inspecting the plant regularly for any infestation and removing the larvae from the plant. Chemical means involve the use of chemicals in the control of the larvae infestation. Some of the chemicals used include Bacillus thuringiensis aizawai (Xentari), Azadirachtin (Azatin), and Bacillus thuringiensis kurastaki (Dipel). Biological means involve the use of parasitic wasps in the control of larvae (Whipker, Cloyd and Campbell).
The main chemical method that has been employed in the control of cabbage worms is the use of Bacillus thuringiensis or Bt spray. The method has even been incorporated in the plants such as maize. The plants that have Bt gene incorporated in them are referred to as genetically engineered plants and lead to the production of crystal (Cry) proteins or toxins (Hellmich and Hellmich). A unique feature that is found in Bt is that there is a release of protein crystalline structures, which have an effect against the cabbage worms. The proteins are producing the sporulation phase of the bacterium. Different proteins have different activities on a given insect type with the main pests that are targeted using the Bt insecticides are the stem borers, bollworms, budworms, as well as the leaf worms in crops and grains (Shelton).
This study aimed at offering familiarization with the process of conducting and interpreting scientific experiments through the study of the effects that Bt has on two different varieties of kale, Red Russian kale and Toscano kale. The use of Bt in the management of larvae infestation has been reported to be successful (Kaya, Burlando and Choo). It was thus hypothesized that there was a significant difference in mean damage between the control and Bt treatment on Red Russian kale and Toscano kale.
Materials and Methods
The experiment was done following the protocol that is explained in the laboratory manual. The number of samples that were used in the control experiment for the Red Russian variety to check for damage was 115 while the samples in the experimental Red Russian were 111. A sample size of 104 was used in the determination of the damage in the control experiment of Toscano variety while 109 were used in the experimental Toscana sample. Monitoring of the damage was started on 26-March and done for the second time on 9-April the third time of monitoring the damage was done on 16-April with the last time being done on 23-April.
The number of damage was determined in each of the sample set was determined in the four days and the damages recorded in Table 1 below. In most of the groups the number of damage increased gradually with the control group having a higher number of damage when compared with the treatment group.
The average damage for the trial number 1 and trial number 2 was calculated and the average damage used to plot a graph of average damage against the day the damage was monitored.
Figure 1: A graph of average damage against the day the damage monitored
The results obtained were summarized in the Table 2 below. The number of samples that were used in the control and experimental Red Russian variety were 115 and 111 respectively. These gave a mean of samples destroyed as 1.6 in the case of the control Red Russian group while the experimental Red Russian had a mean damage of 1.5. The number of samples that were used in control and experimental of the Toscano variety was 104 and 109 samples respectively. The mean damage that was recorded in the two groups was 1.8 in the case of the control group and 1.4 in the experimental group.
Using the data collected, a Mann-Whitney U Test was done to determine whether there was any significant difference between damage that was recorded in the treated group with the damage that was recorded in the control group. This was done both in the Red Russian variety and the Tescano variety. The p value in the comparison of control group versus the Bt treated Red Russian Kale was 0.25 while the p value in the comparison of control versus Bt treated Tescano Kale was 0.047.
One of the most common transformations that have been employed in the development of plants that are pest resistance has been the use of Bacillus thuringiensis or the Bt genes. The presence of Bt gene in a plant enables the plant to produce Cry toxins that are lethal to a number of insect pests that are targeted. Over the years, there has been a great risk for a pest resistance evolution especially in the wild population. The evaluation of this need to be evaluated and its extent minimized. The mechanism of Bt toxin is mainly in the damage of the mid-gut of the insect or worm. The Cry proteins undergo crystal solubilization in the insect mid-gut, and the protoxin is processed by the proteases that are in the gut. The Cry toxins then bind to the mid-gut receptors and the toxin is inserted into the apical membrane in order to make pores or ion channels. There are more than 150 varying Cry proteins identified some including Cry3Aa proteins that target coleopteran insects. Other proteins include the cry1 as well as cry2 families that are mostly effective in the management of lepidopteran species (Schnepf, Crickmore and Van Rie).
The experiment aimed at determining the effect of Bt in the control of damage from cabbage leaves. The comparison of the damage results obtained in the control group and experimental group of Red Russian kale was done using the Mann-Whitney U Test. The p value obtained was higher than the set value of 0.05 which is a 95% probability of the treatment and control being different. This shows no significant between the control and Bt treatment on Red Russian kale. The hypothesis on of a significant difference in mean damage between the control and Bt treatment in the Red Russian kale variety was not attained.
Similarly, the comparison of the damage obtained in the control and treatment group of Toscano kale variety was done using the same test. The p value obtained was less but very close to the set value of 0.05 which is a 95% probability of the treatment and control being different. This shows marginally significantly less damage in the Bt treated group when compared to the control group. The hypothesis on of a significant difference in mean damage between the control and Bt treatment in the Toscano kale variety was no attained.
The effectiveness possessed by the toxins that are produced by Bt against different, specific pest species that attack various plants has been shown in a number of laboratory experiments. The resistance of the Bt has also been shown to result in increase yield. A study on the effect of Bt treatment has been done on the damage extent in P. vitellinae. From the study, the damage recorded on the Bt treated group was significantly lower than the damage that was recorded in the control group that had no Bt treatment (Hjältén, Axelsson and Whitham). There is also evidence that Bt helps in the affect in a negative way the survival, growth and the reproduction of insects such as leaf beetle. The plants that express Bt have also been shown to be resistant against leaf beetle, also known as Crysomela tremulae. In another study that monitored the damage of cultivated sunflower that expressed Bt with the control group, there was a reduced damage in the treated group compared to the control group (Snow, Pilson and Rieseberg).
The experiment may thus be concluded to have successfully tested the hypothesis that use of Bt helps in the reduction of damage of kale by the larvae. This was clear in the Tescano Kale variety. The damage in the experimental group was not different from that of the control group in the Red Russian Kale variety. The variation may have been due to error in the experimental method used.
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