Correlation between traits in two different plants?  What exactly are you correlating it to?

Is this due to an interaction between the plants (the plants evoke the traits of interest in one another)?  Or, are you looking at examples of evolution of the trait due to the same selective pressures placed upon the plants of interest?

You could always study the two plants and the trait and see if there is a strong correlation with any external environmental factor.  

You could also ascertain whether or not certain categories of gene products are expressed/repressed with different variants of the traits in the two plants.  This could indicate whether or not the same network of genes (or even the same gene) are involved in the expression of the trait.  This could be done via sequencing or via hybridization assays (microarray, gene chip) or RNAs expressed.  

Breeding, or selecting individuals from a segregating population based upon variation in the trait, benefits you in that you reduce any "background noise" and allows you to potentially identify - at least in that population - what is principally driving the variation observed in the trait of interest.

Just some ideas.

I also didn't fully understood the question, but Pearson simple correlation will do, if we are talking just about two traits and link among them

thanks a lot James W. Borrone ·thanksssssss

and i know Pearson correlation Velimir Mladenov  a asked about genetic relation