Category Archives: Intraspecific hybrids

Articles about intraspecific Jatropha curcas hybrids.

Heterosis seed comparison

Jatropha hybrid heterosis: 50 fruits in a single cluster

Jatropha hybrid heterosis

50 fruits in one cluster

We are currently observing another impressive result of hybrid vigor in our Jatropha Breeding Program: a six months old hybrid exhibits the first fruit cluster with exactly 50 healthy fruits. The seedling germinated on March 17 (my birthday :-)) and has reached a height of more than 2.5 meters by now. Manual pollination has been conducted 10 days ago.

Among other this hybrid also shows a distinctively superior tolerance to drought stress than both parents. As usual drought tolerance goes together with relative (horizontal) pest resistance.

2 sister plants of the identical hybrid which had germinated in the same week are showing similar impressive fruit counts for their first clusters: 35 and 42 respectively.

CLO7.10xGHLT hybrid

Hybrid fruit cluster

Update: the same fruit bunch 10 days later…

 

 

 

 

 

Update 2: On November 23 we harvested the first fruits from this bunch. Obviously, we were very curious to find out about a possible heterosis effect on seed size and weight. Well, what can I say? It’s another breakthrough really that would deserve its own separate article on this site:

We weighed 15 freshly harvested seeds at a total of 18 grams. This converts into a 100-seed weight of 120g. That’s a new record in our breeding program.

Heterosis seed comparison

Seed comparison with parental accessions

As a matter of completion, the 100-seed weights of the parents:

  • female parent (top left): 90g
  • male parent (top right): 45g.

It will be interesting what we are going to see in the next generations of hybrid crosses. The plant has already been crossed with most of our high quality accessions and also back crossing with both parents has begun. We will definitely report again in the future. 

Heterosis effect showing in seed size

Heterosis increases Jatropha seed weight 100% and more

It has been only a month since we last wrote about heterosis in Jatropha breeding. However, we had not seen then, what we have seen now…

We have harvested a first batch of Jatropha seeds from the intraspecific hybrid exhibiting by far the strongest heterosis effects in leave size and height. And we were up for a real surprise.

We had recently seen 2 scientific reports on heterosis trials with Jatropha in South East Asia describing maximum positive heterosis in seed weight of up to 25%. We therefore never expected to see our highest 100-seed weight increasing so much. Extrapolated from 20 harvested seeds it slightly exceeds 110g. Size can be compared well in the picture above with control being a typical average size seed at a 100-seed weight of 56g.

Our own findings are completely in line with the above mentioned reports, while showing even further potential. We still have to cross those parental lines in our possession with the greatest distance according to our genetic map. As all available results point to the very strong positive correlation between heterozygosity and heterosis in intraspecific Jatropha hybrids we expect that our latest findings can easily be exceeded once all our planned hybrid crosses have fruited.

This latest success supports our ongoing planning for a dedicated heterosis breeding sub-program which could allow for stable, highly superior F1 hybrids within less than 2 years.

 

Jatropha seed comparison

What makes an elite Jatropha cultivar

What exactly makes a certain Jatropha accession an elite cultivar? You can find the term everywhere but a clear definition is usually not given. Therefore I want to explore this subject today and attempt to demonstrate how an answer translates into  the daily work of a Jatropha breeder.

The term itself is simple: elite means something like “better than average” and cultivar is just an abbreviation of “cultivated variety”. But what does it really mean to us?

The most general and holistic objective when breeding for an improved commercial crop is of course always maximum profitability for the farmer. As this is self explanatory only a next level break down of objectives can offer some insight. In our program we use 4 groups of traits which in turn again break down into the real, identifiable traits when observing a selected plant.

The groups we use at Bionic Palm are:

  1. Seed Quality
  2. Seed Yield
  3. Agronomy
  4. Pest resistance.

We are looking for improved traits in all of the above groups. Let’s have a quick look at each group to see some of the aspects a breeder is really looking for every day.

Seed Quality
For us this includes several individual traits, all linking back to profitability of the crop of course.

  • Toxicity
  • Uniformity within the seeds
  • General healthiness of the seeds
  • Chemical composition of oil and cake.

No further explanations needed here I think.

Seed Yield
This is the most relevant for most people discussing Jatropha, but what are we really talking about, when we use the term? 

Many people would just want to count the seeds or go by tons per ha. An approach that would translate into something like number of seeds harvested per plant per year. This again translates into bottom line traits like branching (self or pruning induced), number of fruit clusters or fluorescences per branch, number of fruits per cluster (= number of total flowers in a fluorescence plus male:female flower ratio). Not too difficult to understand, once you know the Jatropha exclusively flowers at the top of a branch.

However, that’s not even half the truth. In our understanding the high level measurement must actually be average amount of crude oil obtained per ha (or acre) combined with average amount of cake per ha.

We have recently taken a closer look at seeds obtained from the various hybrids we produce. A comparison shows significant differences in seed weight and oil content which are actually quite stunning. And the spread is increasing the longer we breed…

Jatropha seed comparison

The typical measurement 100 seed weight varies from around 45g to 98g in our current accessions and oil content ranges from 25% to clearly over 50%. That means with an equal number of seeds per ha I can actually have up to 4 times the oil!

Agronomy

 Lets move on to traits important for agronomic reasons. Many of them are related to the cost involved in farming Jatropha and the most to the ease of harvesting.

There is the uniformity of fruit ripening which determines how many times a picker has to pass a plant per season, then there is canopy structure and size of fruit clusters which determine the ease and speed of harvesting. Other important agronomic traits are self branching (without the need of pruning). Also drought resistance or rather the reaction to water stress is an important trait. We find that there are tremendous differences between accessions. The difference is at what level of water stress a plant stops female flowers, no flowers at all, throws off developing fruits and more. We see a clear pattern of those reactions differing greatly among accessions. I also have to admit that so far the best performers are the weakest in terms of water stress resistance.

Pest Resistance

Many of the common publications about Jatropha suggest that their toxicity would protect them from pests. This is not the case! The most serious pest we are confronted with is the papaya mealy bug. It comes and goes with water stress. There is no correlation with toxicity at all, however a clear correlation with resistance against water stress. And it should be at least mentioned here that the available phosphorus in the soil plays a major role in any plants ability to handle water stress. Therefore the right soil amendments like mycorrhiza can make a huge difference in addition to the best suited accessions if you plan to plant Jatropha in the desert. :-)

I am aware that this review of relevant traits in Jatropha is anything but exhaustive, but I don’t want to bore my readers too much with the obvious. Therefore I tried to point out only a few of the less discussed but important aspects of this fundamental subject on the way to true Jatropha elite cultivars.

The role of heterosis in Jatropha breeding

Today I want to take a closer look at the relevance of heterosis in Jatropha breeding. Heterosis or hybrid vigor, or outbreeding enhancement is “the increase in growth, size, fecundity, function, yield, or other characters in hybrids over those of the parents”. Find more information on heterosis on Wikipedia.

Heterosis effect can be forecasted based on this genetic variability map

Almost 3 years ago we started all our breeding efforts from this genetic variability map created by our friend and advisor Tommaso Barbi working at Geneticlab in Trieste, Italy at the time.

The parental accession base of the Bionic Palm Jatropha breeding program is not a 100% overlap, but we do have quite a significant number of key accessions in our program which are also shown in the map while many others can be linked to one of the clusters genetically or phenotypically.

Simply speaking, crossing more distant accessions from the map increases the likelyhood of significant variability in the hybrids genetically expressing itself in a higher degree of heterozygosity. Another crazy insider term from molecular biology, I know. Heterozygosity describes the amount of differences between corresponding alleles in a DNA sequence. Homozygosity is the term for the opposite situation of corresponding alleles being similar.

It has been found that heterozygosity usually correlates with strong heterosis effects. In the map above a cross between more distant accessions leads to a higher heterozygosity in the resulting hybrids and therefore higher levels of heterosis can be expected. Only about 6 months ago we started to be able to observe different heterosis levels in our hybrids.

The molecular basis of heterosis is still not fully understood. Current believe among scientists is that healthy alleles across numerous genes from one parent compensate for dysfunctional alleles at those genes from the other, distantly related parent (and vice versa for a second set of genes). A plant exhibiting a high level of heterosis would thus be the genetically most healthy.

This explanation fully corresponds with the opposite effect of inbreeding depression. Here parts of the parental alleles become dysfunctional or silenced because there is too little genetic difference between the two parents. The very strong expression of heterosis we observe when crossing a semi-commercial Jatropha accession from Africa or Asia with a wild accession from the center of origin therefore suggests at least a mild inbreeding depression on a very narrow genetic variability in the germplasm originally introduced by the Portuguese seafarers when they first distributed Jatropha around the world.

So far observations are limited to leave size and, at a smaller extent, stem diameter. Over the coming month fruit and seed sizes will become visible too. With the leaves we quite commonly measure lengths of up to 20cm where the usual average is no more than 10cm.

The following picture demonstrates the phenomenon very clearly.

Heterosis in Jatropha breeding can be observed in this intraspecific hybrid plant

The small plant in the front germinated in November 2011 and is a cross of 2 accessions with distinct phenotypic differences but, genetically very similar, they are both from the upper left cluster in the map. The much larger plant behind in the center germinated in March 2012, 5 months later, and represents a cross between the upper and lower left hand clusters. Average leave length is almost double that of the plant in the front and of course the overall size is significantly different.

 A heterosis effect is also visible in many of our interspecific hybrids, but notably less so in those which have a very short seed-to-seed time of less than six months. A behavior which can be attributed to negative heterosis (=shorter seed-to-seed cycle). Interspecific heterosis can be observed in the following picture.

Heterosis in Jatropha breeding

The plant on the far left hand side shows by far the most dramatic heterosis effects. Followed by the next 2 plants to the right with heterosis also clearly noticeable. All 3 happen to be non-toxic interspecific hybrids. Then we see an early flowering and fruiting interspecific hybrid exhibiting no visible heterosis. Similarly at last, on the far right some regular Jatropha can be seen. From left to right we go from high level heterosis to none at all.

In front a rare chili pepper can be seen which is currently tested for drought resistance.

The findings described in this post have been highly unexpected. We are currently waiting for the first seeds from plants exhibiting strong heterosis to mature so we can check seed weight and oil content. Based on the results we will have to decide if we are going to open up a new heterosis breeding route in addition to our current approaches.