http://www.ars.usda.gov/SP2UserFile...t-Kurti/Balint-KurtiJohalMaizeDisResist08.pdf
Please read this article and mainly down to page 3.
It tells you that diseases were found in the clones. So it isn't a false statement.
I just read the first five pages and skimmed the rest, and you have misinterpreted the article. It doesn't say anything of the sort.
Part 1 (the introduction) is just a general overview on maize and maize loss and why it is important to breed/clone disease-resistant lines, and even endorses the use of disease-resistant plants when it says, "Losses have tended to be effectively controlled in high-intensity agricultural systems where it has been economical to invest in resistant germplasm..." In other words, the use of cloned, disease-resistant lines prevents losses, it doesn't cause them.
Part 2 is just a general overview of the two types of gene-conferred disease-resistance in plants, quantitative and qualitative.
Part 3.1 I think is where you got tripped up. Part 3 is talking about early studies in plant genetics--that is, studies from the 50s, 60s and 70s on genes
naturally found in plants/maize. This section is not about bioengineering, or cloning. It's about naturally occurring genes in plants, plants that were bred just like plants have been bred by humans for thousands of years. What it's talking about is cms-T maize--cms just means cytoplasmic male sterility, which is a trait that means the plant can't produce pollen on its own. This is a naturally occurring trait that was discovered over 100 years ago (see
http://www.isb.vt.edu/articles/sep0502.htm). CMS occurs in over 150 plant species naturally. The T simply refers to a specific subtype of cms maize that was discovered in Texas in the 1950s (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC160361/pdf/051285.pdf). CMS is a useful trait in maize because maize with this trait does not have to be
detasseled, which makes the harvesting process quicker, more streamlined, and more efficient (
https://en.wikipedia.org/wiki/Cytoplasmic_male_sterility).
Section 3.1 goes on to say that after this cms-T maize was discovered and put into widespread agricultural use, it was found to be susceptible to a specific pathogen because cms-T maize contained a protein called URF, encoded by the
T-urf13 gene.
So this section has nothing to do with modern cloning or bioengineering techniques. It's only about some early studies that helped scientists figure out what kinds of genes facilitated disease in plants.
The rest of the article goes on to discuss disease resistance and plant genetics and molecular mechanisms of maize in more depth, and concludes by saying that modern bioengineering/cloning will be invaluable in creating plants that are resistant to loss and disease.
And also you have to realize Wikipedia is NOT a reliable source. Anybody can change the data on the page whenever.
Actually, Wikipedia is a very reliable source as long as it's not a page about someone/something very obscure. Pages on well-known and popular people/phenomena have high quality control, and even if somebody makes a false edit, it's changed back extremely quickly--not to mention that there tend to be so many sources that it's easy to cross-reference any given part of an article.
Seriously, Wikipedia helped me more than most of my textbooks when it came to science classes. My old lab PI used Wikipedia almost exclusively whenever he forgot something or wanted to explain a concept to us
While it's not a source you should cite in a formal paper (for obvious reasons), it's a great resource to get an overview on a topic and a great jumping off point for further research.
By the way, if you want some ammo in your argument against cloning of genes into plants, you should read up on Bt/Starlink corn:
https://en.wikipedia.org/wiki/Genetically_modified_maize#Safety_issues
edit: of course, I think this is getting further and further from the OP, which is about cloning
life, not just genes. Muhti, if you want to continue this, I encourage you to make a new thread about cloning specific genes into plants/animals