Sunday, 22 February 2015

Tomatoes: Potato Leaf vs Regular Leaf

People often talk about regular leaf tomatoes or potato leaf tomatoes, I get a few questions about this so I figured I would write a post explaining what is meant by these terms.  I have also seen one place sell a variety of tomato that they call "potato leaf tomato" and I find this confusing as there are many varieties of potato leaf tomatoes, I am growing 4 of them this year myself.

Have a look at these two leaves, they are both leaves from tomato plants.  Please ignore the yellowing, that has nothing to do with leaf type, that leaf is a bit older.
Potato Leaf compared with Regular Leaf
It is not too difficult to tell them apart, the leaf on the left looks like the leaf on a potato plant, the leaf on the right looks like the leaf on most varieties of tomato.

Regular Leaf (RL) tomato
Regular Leaf (often abbreviated RL)
This is the typical leaf type that most people are familiar with, most varieties of tomato are regular leaf.  The leaf edges are serrated quite a bit.  There are a lot of variations on this basic theme in terms of the width/length of leaf depending on the specific variety, climate and growing methods.  There are a few other variations such as angora, variegated etc but they are not easy to come across in Australia so I wont talk about them.  Some leaves are very narrow and are sometimes called 'dissected', others are wispy or droopy or look like the foliage of a carrot.  These are easily recognised from a distance even by my 5 year old as the leaves of a tomato plant.  All of this is referred to as Regular Leaf (RL).

Potato Leaf (PL) tomato
Potato Leaf (often abbreviated PL)
These leaves usually have very few interruptions of the leaf edge.  They are fat and large leaves. Newly germinated seedlings sometimes don't show their PL nature until they are a few inches tall, others show it as soon as they grow their true leaves.  PL leaves often have a thicker cuticle than RL leaves or a higher density of trichomes (which are tiny little hairs on the leaf).  Some claim that makes them more tolerant of foliage diseases but I have seen no proof of this.   Leaf shape can be different on a single plant with some showing more or less smooth edges, all of this is normal for PL.  Scientists have divided the PL leaf forms into various different classes but few of them are available in Australia and it makes no real difference so I wont write anything about them.

What is the deal with growing Potato Leaf tomatoes?

Some people claim that potato leaf tomatoes taste better, unfortunately that is a half truth.  Almost all Potato Leaf tomatoes are heirlooms and generally heirloom tomatoes taste great.  Some tomato varieties have a Potato Leaf version as well as a Regular Leaf version, I can not taste any difference.

People often claim that Regular Leaf tomatoes do not cross pollinate while Potato Leaf tomatoes will cross readily.  Unfortunately this is not at all true.  Most modern bred varieties of tomato will not cross pollinate easily (literatures states around 5% crossing without intervention when being grown side by side), almost all heirloom tomatoes do cross pollinate, some far more than others.  As most Potato Leaf tomatoes are heirlooms people have got themselves confused here.  The tomato I grow that crosses most readily is Reisetomate, it is a regular leaf plant.  It cross pollinates so much that I even grow it in a separate garden to all my other tomatoes.  Try not to be fooled, Potato Leaf does not necessarily mean heirloom, just as heirloom does not necessarily mean Potato Leaf.

Potato Leaf is considered to be a recessive trait.  When breeding new varieties if Potato Leaf is crossed with Regular Leaf then all the seedlings will be Regular Leaf.  This makes it useful to see early on  if the cross has worked or if the flower self pollinated and the plant is worth growing on or not.  If growing different varieties of tomato then Potato Leaf can also indicate early on if that particular seed has remained pure.  If a potato leaf variety grows regular leaf the chances are high that it has crossed.  Some potato leaf varieties do occasionally throw a regular leaf plant even when they have not crossed, so things do get a little confusing here as there is a little more to it than a simple dominant/recessive trait.
Potato Leaf tomato
"Julia Child" a great potato Leaf tomato variety
I have heard theories about potato leaf being more resistant to insects and regular leaf being more resistant to insects and visa versa, but I have found nothing conclusive that back up this.  Potato leaf would possibly restrict airflow more than regular leaf, so it is possible that potato leaf would face more mold problems in damp environments but again I have no proof that confirms or denies this.  I live in an area of low humidity, so it doesn't matter to me in the slightest.

I have also heard anecdotal evidence that potato leaf varieties are more 'hungry' than regular leaf as they require more resources in order to build more leaf, again I am yet to find any research that either backs or refutes this claim.  It kind of makes sense to me, but some of the largest tomato plants I have ever seen have been regular leaf, I assume they used a lot of resources to grow that large.  I have one regular leaf tomato that grows a large shrub to about 8 feet in every direction, it is surely using a lot of resources to build all of that stem.

Some people think the Potato Leaf plants look nicer, I certainly think they look more ornamental and would not look out of place in a flower garden.  To be honest, I wish that I had more potato leaf tomato varieties as I simply like the look of them.

At the end of the day though the leaf shape makes no real difference to me and I doubt it makes any real difference to taste, growth rates or anything other than aesthetics, so I base my planting decisions on the taste of the fruit and performance of the plant.

I do sell seeds of some heirloom tomatoes as well as perennial vegetables on my for sale page, you should have a look if you are interested.

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